Thronebreaker: The Witcher Tales

Firstly, be aware that there are a variety of reported bugs when it comes to this Achievement as of the time of writing. Seemingly carried over from the original PC release, it is common to see the Golden Chest count display inaccurately when ending a Chapter/checking in with the Rider in your camp, or for command icons to bug out making Chests unopenable.

Many of the 42 Chests are easily discovered by scouting the map (purchase the Watchtower from the Workshop in your camp immediately to help generally with finding things and pay 50 gold over and over to fill out the map), but some require specific actions or the provision of Treasure Maps to be able to be located. You must get all of the Chests in a single play through and if you experience any of the bugs with miscounting of Chests the Achievement will not pop at the end even if you opened them.

If you are thorough in your play through, you can't really miss any of the Maps/Chests, but note that you must accept Maps if they are offered to you by NPCs - there are two specific instances in which a dishonourable choice must be made to accept a bribe with the Map and a few others where you must pay for/take a Map from other travellers. There is no alternative way to obtain these locations - if you do not get the maps you cannot get the Achievement.

For those who would prefer to simply follow along, Game Pressure has clean maps for each Chapter highlighting the locations of the Chests and the corresponding Treasure Map locations where appropriate: https://guides.gamepressure.com/thronebreaker-the-witcher-ta...

If you play on Adventurer difficulty so that you can skip battles and skip all dialogue options and unnecessary content, you can speed run the 5 required Chapters in about 80 minutes, so if you do have a problem with bugs etc., I recommend just enjoying the game and the story and mopping up in another run through. Sadly, because of the prevalence of bugs in the current state, it took me 4 play throughs.

Fortunately, this achievement is a piece of cake as soon as you buy the watchtower Upgrade in the workshop at the command tent section. As soon as you do that, open your map. By pressing Y you can now invest 50 gold to scout the map, which uncovers a few collectibles. After investing ~1500 Gold, everything in the map is discovered, showing you the locations of the treasure chests, points of interests and loot.

Make sure to talk with every npc, since some will give you maps if you did something for them.

EDIT: 2nd Map Aedirn has a bug which is when you try to leave the map and it says 8/9 chests although you found every all the nine.
I will edit this solution again if it makes the achievement unobtainable right now or not

EDIT 2: Finished the game with 41/42 although I collected all chests. Someone else unlocked the cheevo though, so it must be a bug appearing on the heavy amount of crashes

Haven't seen this posted elsewhere but I just wanted to note that you can roll back a save to an earlier point. From main menu, go to 'Load Game' and hit 'Return To...' on the region you missed a chest.

I thought one in Angren glitched for me, turns out I just didn't have the map. Used the Return To feature to go back, lowered the difficulty to skip battles and skipped dialogue, full chest completion. You can then do this until you're caught back up, if you want to play normally.

The fandom.com maps only show the chests, therefore are much easier to understand than the ones if seen in here. Just check the stats (leftmost guy in your camps tavern) b4 you travel to the next area. With this, the missable achievment becomes "unmissable"

https://witcher.fandom.com/wiki/Thronebreaker_treasure_maps