Mine is probably the Liberty City Minute achievement for Grand Theft Auto IV. I think technically you have 30 hours to beat the main storyline but I managed to power through and beat the entire game in one sitting.
Achievements were only added in after an update a couple years ago (when they removed the dated Games For Windows Live DRM that made the game pretty much impossible to play without modding) so it’s technically not the rarest for the game. The achievements for getting the highscore in QUB3D and flying underneath the bridges are even more rare but I’d argue they’re easier to get.
What Steam achievement are you most proud of?
Is there one that took a lot of time to get? Did you have a good time with friends? Was it an achievement you struggled to get on other platforms when you were younger?
Regardless I’d be interested to hear about it.
There are some tricks you can do to make this one a bit easier. I played on a set seed, first planning a base for it in editor mode, and then copying the entire base as a blueprint. You have to play with biters, but you can set their spawning area to be far enough away that you won’t need to interact with them. I also made a new save file for each major milestone in the base, so if I didn’t reach the end quick enough, I could try to go back to a previous segment that I thought was slow and do it faster.