Crusader Kings III

1) Introduction
The main reason why many players don't unlock this is probably that it takes a lot of time and that players get bored with their playthrough before they get there, because they already built a vast empire and there are no real challenges left. If you actually play to 1453, you don't have to optimize research to get this, though it is possible to fail if you continuously neglect research and play an underdeveloped culture. To help you complete the research before the playthrough gets boring, here is a guide how to do this as fast as possible.

Unfortunately, there is no shortcut to do this super fast, because the late medieval era is unavailable until the year 1200, so it is literally impossible to research any of the 14 late medieval technologies before that year. I unlocked the achievement in 1281, starting as the Italians (Matilda di Canossa) in 1066. During the campaign I also recreated the Roman Empire. I recommend picking another long term goal like this to work on to have a fun campaign. There is no need to do a boring "research only" playthrough, prioritizing research won't keep you from building a vast empire, it can actually be quite helpful for that.

2) How do the research mechanics work?

To optimize research, we need to understand the research mechanics. You can see all of your cultural innovations and their progress in your culture menu (click on the candle symbol to bring it up). You don't just research one innovation at a time, you actually have a small chance to gain a bit of progress in every innovation that belongs to an era (tribal, early medieval, high medieval, late medieval) that you have already reached. The base chance to gain progress is so small though that it often feels as if you were just researching one innovation at a time.

2.1) Progress chance
The base chance to gain a bit of progress each month is only 5% for each technology. There are two things to boost this chance massively for single innovations: Exposure and cultural fascination.

Exposure occurs when you intermingle and have a high mutual acceptance with a culture that has already unlocked that innovation. The exposure will give you a flat + 40% on your chance to gain progress.

The cultural fascination is selected by the leader of the culture and gives a massive bonus to the progress chance for one innovation at a time. The size of that bonus is variable and depends on the culture leader's learning skill as well as some other possible boni that I will list below. It can be as low as 0% (if the culture leader is a complete moron) and can get as high as 100% (technically, the bonus can even get beyond 100%, but you won't get more than one tick of progress per month for that, so 100% is effectively the limit).

The leader of a culture is the landed noble of that culture who has more counties of that culture within his realm than any other lord of his culture (or her, I won't gender because for most cultures in the game male rulers are the default, but unless explicitely stated otherwise, everything works just the same for female landed rulers), regardless whether those counties are governed by himself, his vassals or vassals of his vassals. The culture leader doesn't have to be independant, he can be the vassal of someone from another culture. Your first goal to do effective research is to BE that culture leader, otherwise the fascination will be selected by an NPC and its impact will depend on their skills instead of yours.

The basic factor that decides how impactful the fascination bonus is, is your learning score. I think it is double your learning score in percent. The impact can further be increased by the following:
- the scientific perk (starter perk of the scholar skill tree) gives + 20%
- a university building within your personal domain (not just your realm!) gives + 5%. This bonus stacks for multiple universities
- if (and only if!) your culture has the "philosopher culture" tradition, learning education traits and the scholar trait (which you can get as the finisher perk of the scholar skill tree) also give a bonus to your cultural fascination. (+10% for scholar, + 5% for each star of the learning education trait, i.e. +20% for mastermind philosopher.
- holy site bonus: catholics get a 5% bonus from the cologne cathedral, as long as any catholic holds that holy site. Orthodox get a 15% bonus from Constantinople as long as any orthodox holds that holy site. Both of those boni obviously also apply for other faiths and homebrewed heresies who regard those places as holy sites as long as their faith controls them.

Exposure bonus and fascination bonus can stack, but you should always try to avoid stacking those two unless you need that one innovation really urgently. Your overall progress will be faster if you have good chances in more than one innovation at the same time and the exposure bonus will be used up once you unlock that specific technology, with no guarantee that you will get a new exposure bonus on something else. Also, you will likely be able to get your fascination bonus up to more than 55%, so the excess chance would be wasted if you stack it with exposure. Thus better let that technology with the exposure bonus "unlock itself" at a slightly slower pace of 45% and use your fascination bonus on technologies that don't have exposure.

2.2 Progress size
Each innovation has a progress bar of 100 to fill. The size of each monthly tick of prgress (if you get one) is base 0.3 plus 0.2 if the technology is from a prior era (e.g. from early medieval when you already reached high medieval) plus a variable bonus that depends on the average development of all counties of your culture. For this bonus, it doesn't matter whether those counties are within your realm or not.
The size of your culture doesn't have any impact at all! A culture that has only 3 counties with an average development of 20 will have a bonus that is twice as large as a culture that has 20 counties with an average development of 10.

2.3 Unlocking a new era
A progress bar to unlock the next era will automatically appear once you have researched at least half of the basic technologies of the current era (the special regional and cultural technologies of that era don't count!) and have reached the minimum date (which is 1200 for late medieval. I don't know the exact minimum date for high medieval, but if you start in 1066, you will already be able to unlock it). Always prioritize researching the innovations of your current era until you have enough to progress to the next era, before you research the leftovers from the previous era, so that you get that 0.2 progress bonus and the base chance to advance all of the technologies of the new era too as early as possible. As an additional benefit, you are quite likely to get an exposure bonus for those less needed early age innovations if you save them for later.

2.4 Instant technology unlock by creating a hybrid culture
If you have the royal court DLC, you can create a hybrid culture with another culture in your realm that has a different cultural heritage (so e.g you can't hybridize Italian and Sicilian, because they both have Latin heritage) and a high enough cultural acceptance (I think 40%). The newly created hyrid culture will instantly unlock all the innovation progress that both "parent" cultures have, which can be a significant shortcut. Keep in mind though that only your personal domain will acquire that new culture at the start and make sure that the average development of your personally held counties is equal or higher than your overall cultural average, otherwise creating the hybrid culture might do your progress more harm than good.

3) Which starting culture to pick?

You should start in 1066 with a feudal culture. Starting in 867 won't give you any benefit for this achievement because you can't unlock the late medieval era prior to 1200. It is possible to research every earlier innovation until 1200 when starting in 1066 and working on your research well, so starting earlier would just add more waiting time to your game.

There is no single best culture to pick. You'll want to pick a culture that meets the following criteria:
- is already in feudal age
- doesn't have the bellicose ethos (because that ethos is incompatible with the philosopher culture tradition)
- has counties with a very high development and/or only has very few counties (which makes boosting the average development easier)
- has a possible building spot for a university inside their counties or close to them

Among the lesser used maps (plus sign bottom right) there is a map that displays development and a map that displays economy and all existing and potential special buildings, so you can use those two maps to check whether your favorite cultures meet those criteria. Among the best ones are the Italians (the related cultures Cisalpine or Sicilian aren't much worse either, but Italian has the highest average development to start), the Egyptians, the Bahranis (Northwest Africa) and some of the Indian cultures. Pretty much all of the Iberian cultures except for Castilian (bellicose!) are decent choices too, if you want to go for some of the special Iberian achievements in your playthrough. The Greek are surprisingly just a mediocre choice. They have some of the highest developed counties of the game, but are also spread out wide over underdeveloped hillside counties and have no university building spot. But if you have the royal court DLC, it could be an OP move to start as the Byzantine empire, conquer northern egypt early (including the university of Cairo), gather the highest developed counties of both cultures in your personal domain and then create a greek-egyptian hybrid culture.

4) What to do?

4.1) Quick overview (more in depth advice on some of the points below)

- If you aren't already the leader of your culture, become the leader ASAP by conquering more counties of your culture

- breed your heirs for the genius trait. If your starting character is already married to an average spouse without special traits, try to get rid of the spouse (divorce or "unfortunate accident") and marry one who has the genius or at least the intelligent trait instead (genius can be quite rare at the start of the game).

- research the high medieval "divine right" innovation ASAP, which allows you to raise your crown authority to absolute, which in turn allows you to freely pick your heir among your eligible offspring (including daughters). Whenever possible, pick a genius with a learning education trait (priority in that order)

- get the "scientific" perk for your starting character as well as any new heir as quickly as possible, so you can profit from its bonus for the whole duration of your reign. If your character doesn't have the learning education, you can either start with a learning lifestyle anyway and later switch back to the lifestyle that fits your education or you can do a bit of travelling and get the necessary 1000 learning lifestyle XP by visiting points of interests on the map that provide them.

- push your character's learning attribute as high as possible (you can stop at 48 though, more won't help ;-)).

- seize a county that has a building spot for a university for your personal domain early and start pushing its development by having your steward further development there. You'll need a county development of 30 and the minimum fame level 4 (exalted among men) to build a university. If that county isn't already of your culture, it might benefit your development average to convert it to your culture first, although that isn't necessary to use the benefits of the university. Once you have the university, make sure this county stays in your domain upon inheritance (consider making it your capital, as long as you are stuck with partition sucession)

- establish the "philosopher culture" tradition. Establishing a new tradition in your culture (by clicking reform culture in the culture screen) costs a lot of fame, unmodified I think it's 7000 for this specific tradition, so do the usual things to accumulate fame and save it up.

- get the first dynastie legacy in the "blood" category and the first two (bountiful loins and studious youth) in the "kin" category. The latter greatly increases your chance for good education traits for your children.

- grow the average development in the counties of your culture by having your steward increase county development whenever possible and/or convert some select counties with very high development to your culture. Build county upgrades that provide a bonus to development in counties of your culture (the most effective ones are windmills,water mills and caravanserai). Avoid converting counties with low development to your culture, let them keep their own culture and increase the cultural acceptance instead.

- select your cultural fascination with care. Prioritize current era over previous era, avoid picking innovations that get already boosted by an exposure bonus and don't sleep on those innovations that increase your development and raise your maximum development cap.

- try to get your hands on artefacts that boost lifestyle progress and/or learning score (usually book artefacts, also some holy relics. This is easier if you have the royal court expansion, so you can use and craft court artefacts, but there are some trinket artefacts with such properties in the basic game, too)

- unlock traits that give you health boosts and generally try to avoid undue risks to have your characters reach a high age (because they tend to have better learning scores at a higher age after accumulating various perks and you want to make use of those for as long as possible).

4.2) How to effectively breed for genius

To get this highly efficient philosopher king who is good at everything and has an absurdly high learning score to boost your research progress, you'll have to work for it even before he (or she) is born. The first thing you want to get is the congenital genius trait, which gives you a plus 5 to each skill starting from age 0, which in turn greatly increases your chances to get a good education skill. The trait also boosts your lifestyle XP gain by 30%, which helps a lot when you need to pick up perks from a lifestyle that doesn't match your education trait. If you create a custom starting character in the ruler generator, give yourself that trait even if you have to lower other scores for it to stay within the limit for achievements. If you start with a historical ruler, try to at least get a genius spouse right away.

The genius trait is very rare to occur at random, so if you want to constantly marry your genius kids to genius spouses to ensure a lineage of genius rulers, you'll likely have them marry cousins quite often. This isn't as bad as it sounds, you can do that quite a lot until the horrible inbred trait occurs, especially if you have several lineages of relatives with the genius trait to chose from. Avoid avunculate or sibling marriages though, those will create negative congenital traits much more quickly than cousin marriages. Picking up the "strong blood" dynasty legacy also helps to counter the negative impact of inbreeding. To get a large enough gene pool of genius relatives, try to marry any genius and/or intelligent offspring to spouses who share that trait, even if that means you have to pick landless lowborns over spouses that would provide strong marriage alliances.
If you have a child who "only" has the intelligent trait, marrying them to a spouse who also has "only" intelligent will get you better results than marrying them to a genius. Intelligent + Intelligent always produces at least intelligent with a high chance to reinforce the trait up to genius. Intelligent + genius are treated as two separate traits (just like marrying intelligent e.g. to beautiful), i.e. the child has a chance to inherit either one of the traits, but can also end up inheriting none of the two!

To make sure you find those genius spouses, don't start looking when your heir is already sixteen. Genius children, especially children of landed rulers, are highly sought after and NPCs will usually get them betrothed at a young age, so you want to marry your heir to a genius spouse his age without having to murder their fiancees first, arrange a betrothal when he is still a child.

4.3) How to educate your heir well

When educating your heir, you obviously want to set the education focus on learning education, but you should only do so if your child gets a matching childhood trait at age 3 (curious or pensive). Having the philosophy culture tradition increases the chance to get pensive children, otherwise the childhood trait is random. Don't force it if the child doesn't have the fitting education trait, you can still get a high learning score and be effective at research with another kind of education. Your ruler will be overall more effective with a strong other education trait than with a bad learning education trait that resulted from educating him with disregard for his talents. If your primary heir turns out to be entirely bad at learning, you can still designate another heir by using absolute crown authority (or, if necessary, by disinheriting children, making them monks or forcing them to be knights in very risky battles).

During childhood, children will gain random skill points that often correlate with high skills of their guardian, so always pick a guardian who has high learning, if you don't educate them yourself. When you have a chance to influence their character traits, pick those that raise or at least not lower their learning skill. If you don't educate them yourself, they are likely (but not guaranteed) to pick up character traits their guardian has.

Sending a child to university increases their chances for the best education trait, but it is prohibitively expensive. Most of the time I didn't do it, since having a genius child educated by a genius guardian is usually good enough to get the 4 star education trait.

A guardian who has the "pedagogy" perk from the scholar skill tree will increase a random attribute of the child by 1 to 3, often it is the attribute of the education focus. A parent who has the "groomed to rule" perk from the family skill tree (diplomacy) will give each of their children 1-3 random skill points, regardless whether he is their guardian or not. This does work retroactively even if your children are already adults when you unlock that perk.

Child rulers experience special random events that can increase their skills and can use the special "meet peers" event, which also gives opportunities to hone their skills. This applies to NPCs as well as player characters, thus it is often beneficial to give your heir a secure profitable fiefdom to rule already below age sixteen. A genius ten-year old will already have better skills than many adult NPC vassals anyway. Just better don't give them vassals yet, because children have restricted options for diplomacy and adult NPC vassals are very likely to rebell against a child liege.

At the very least when the heir has reached adulthood, make sure they have something to do, give them land to rule and/or jobs in your court. Landed rulers develop their lifestyle perk experience much faster than idle courtiers. A neat trick to "educate" your young adult heir further is to force him to be a knight during peacetime and then have him travel alongside you by using the "train knights" travel option that is unlocked by having a military academy (this only works if he is one of your three worst knights, but if you have a sizeable realm with many experienced lords, chances are that your 16 year old youngling will be among the worst knights). He will not only gain prowess and possibly commander traits or the blademaster trait, he will also gather experience for the traveller trait and the pilgrim trait (if you take him on a pilgrimage).

4.4) How to increase your learning score as an adult character

Did you think I was joking earlier when I said you can stop at 48 learning? If so, you should read this paragraph ;-). Yes, 48 learning and beyond is possible, my record character even made it to more than 80.
To gain more learning as an adult character, you can do the following:

- have a spouse with high learning and have them do the patronage counciller task.

- get the traits "scholarly circles" and "learn on the job" from the scholar skill tree. The first one increases your learning for 2 for each level of devotion (so that is up to 10!), the latter increases all of your skills by 20% of each your councillors primary attributes (which is another 3-5 points of learning if you have a skilled court chaplain.) The finisher perk scholar is worth another 5 points. If your heir has already unlocked learning lifestyle perks by the time he becomes your player character, remember that you can redistribute those once if he has invested into the wrong skill tree.

- travel around and go on pilgrimages to max out the traveller and the pilgrim trait for another 5 points of learning total (among other benefits). Travelling also triggers a great variety of random events, some of which allow you to increase your skills or get temporary modifiers that increase them or acquire helpful artefacts.

- try to get the character traits herbalist and wise man. You get a chance for this during random lifestyle challenge events that occur during the learning lifestyle (the herbalist event most likely during the medicine lifestyle, the wise man trait most likely during the scholarship lifestyle. Visiting the intellectual center of your religion for sightseeing during your travels (Rome for Christians, Baghdad for Muslims) also gives learning education characters a chance to acquire the wise man trait or get additional learning skill points.

- try to get your hands on artefacts that boost learning and/or lifestyle experience. The most common one in the base game are the "bejeweled scriptures", a trinket which boosts your learning for 1 per level of devotion. Multiple of those do stack. This is even easier if you have the royal court DLC, because you can comission court book artefacts to be crafted instead of waiting for random events that give you the right ones.

- having any university in your personal domain increases your learning by 1 per level of fame. Multiple universities stack. Some select few of them also boost one additional attribute the same way (Intrigue in Siena, Diplomacy in Cairo).

- doing the (expensive and time consuming) university visit event can increase your attributes and has a chance to improve your education trait by one star (including the possibility to get a fith star if you already have four). Not sure whether that is in the base game by now or only available with the wards and wardens DLC.

5) What other achievements to get?

During the same playthrough, make sure to fully upgrade a duchy building (which requires late medieval technology) to get the achievement "monumental" and to acquire and develop a mining county up to 60 income (which also requires late medieval technology upgrades or at least is very very hard to achieve without those) and move your capital there to get the "King of Gold and Iron" achievement.

I unlocked this around the year 1400 with the Italian culture, which I switched to as it was much more advanced than my original Norman culture. If using such an advanced culture, you should have it by the game's end if you continuously research the highlighted innovations.