Assassin's Creed Valhalla

This achievement requires you to collect all wealth, complete all mysteries, and collect/complete all artifacts on all five maps in the game (all of England, all of Norway, Vinland, Asgard, and Jotunheim). If you synchronize all viewpoints in the game, this will reveal all wealth and mysteries on the map. Unfortunately, artifacts are only revealed by either going close enough to them on the map (usually around 450m or so), paying the cartographer in your settlement (once you build his building, but this is only good for England), or paying money to one of the random NPCs around the area with a question mark above their head (which again is only good for England). I personally found that, while taking care of all of the wealth and mysteries in a given region, I ended up close to enough to artifacts to take care of around 98% of them without any issue. There are, unfortunately, a few artifacts in England that you may not end up traveling near enough to have them marked on your mark. Because artifacts aren't marked on your map unless you're near, I highly recommend taking care of any white dots on your compass that you come across during your travels. At a minimum, go close enough to reveal what the white dot is, and it'll stay marked on your map.
 
For whatever artifacts you're missing, check out THIS LINK over to an interactive map at IGN, which will help pinpoint what you missed. To cross-check with your own ingame map, for every wealth, mystery, or artifact you've done, there will be a little black X on your map, allowing you to know for sure if you've already gotten a collectible there. For wealth, especially in Jotunheim, make sure you do all World Events and story arcs in that area, as sometimes wealth becomes available (or is much easier to get) after you've done a quest or World Event in that area.
 
The vast majority of the collectibles are very easy to complete. I highly recommend waiting until you've obtained the Incediary Powder Trap ranged ability before bothering with collectibles, especially artifacts, as a ton of Roman masks are hidden behind destructible walls, and this ability negates the need to hunt down those explosive red vases, making the difficult trivial. There is another ability, Dive of the Valkyries (a melee ability) that allows you to break open a barred door from the front instead of finding a way around it or a way to shoot it open from behind. This again makes collectible hunting far more efficient. Both of these abilities' Books of Knowledge can be found in Grantebridgescire near the beginning of the game.
 
Glitch Information
I would now like to cover some information on common glitches I've come across or read about or have seen reports about.
 

• Reloading an earlier auto save is the best way to take care of bugs related to World Events that won't progress/complete, wealth that won't collect, artifacts that don't seem to be there or can't be interacted with, etc.
• There are sometimes World Events that will say "You must be anonymous to interact" to complete the quest, even though you are anonymous. You'll need to reload an auto save for this, or you could fast travel away to reset the World Event and then come back and start it over again.
• There is a wealth in Vinland that has a tendency to not count/mark off as complete, on a large enemy in the western fort. This method of forcing it to count works, as I had to do it myself to get it to count for me. Full credit to the person on reddit who figured it out (since it is a ridiculous method, but it does work). Kill the enemy (and others in the fort that are attacking you, if need be). If you don't get the wealth from him, or you do but it doesn't mark as complete, assassinate him ( on his limp body), and then carry his body out of the fort through the entrance he was patrolling near. You should spot two enemies off to your left with Odin's Sight. Put the body on the ground and use an Explosive Trap on it (you'll need to obtain this skill from the skill tree, on the upper left side of the yellow tree). Whistle to the enemies so they come over, and let them set off the explosive trap. Now kill both enemies. Once they're dead, quick-save your game (hold  and press ). Now quit to the main menu. From there, choose to Continue your game, and you should be outside the fort where you saved, but the enemy with the wealth is spawned back in the entrance. Kill him (preferably shoot him with arrows, if you have a bow), and then loot him. You should get the wealth and it should count.
• The cairn in Hordafylke, in northern Norway, called Torghatten Rock, is notoriously glitchy. It is very simple to complete, as you can simply stack three of the four flat rocks on each other to reach the needed height. The problem is that it either won't let you validate your solution, or you'll be able to validate but when you do, it doesn't mark off as complete and you don't get the "Cairn Complete" message along with your skill point. The latter problem is the one I ran into, but the solution is the same. Head to the cairn and interact with it. Stack up the three flatter rocks such that they aren't high enough to reach the end point. Hold  to quit while they are stacked. Quick-save your game, then quit to the main menu. Continue your game and you'll be back at the cairn with three rocks stacked. Interact with it, and wait for the dialogue to finish. Put the fourth rock on top, and you should be able to successfully complete this cairn.