Frostpunk 2

Note: I did this on Officer difficulty because I wanted a little bit of a challenge and I underestimated the difficulty of this achievement in particular. It is not necessary to do it on this difficulty and I actually recommend you do it on the easiest one, but this guide will be based on my experiences at this difficulty.

The main hurdle with this achievement is that you only get 1 steam core (a fact that I completely forgot going into this), so you cannot make use of a lot of infinite production structures. I highly recommend you get the adaptive generator upgrade, to max out coal usage (also good if on a map with steam deposits). I keep mixing up the second upgrade to optimize heat usage with the first upgrade that just uses all heat resources in my head. If you have steam deposits, I still think it's a good investment, otherwise save it. I wasn't able to get it to spawn, probably because I was combo-ing this achievement with Consistency and went down the Progress zeitgeist. If you also can't get it to spawn but are on a map with an oil deposit, you can do it with the oil pump upgrade but hold off on building it until you completely run out of coal, because the oil pump upgrade only takes oil and is irreversible, so any remaining coal will be rendered useless. Regardless, you'll want to make your fuel last as long as possible, so sign anything that even indirectly reduces heat demand (like increased housing) and plan out your districts to optimize heating hubs. If you're still having trouble getting your oil or steam districts to meet your needs, try spamming Stimulants Manufactories on industrial districts, which provide production efficiency and are unlocked through the Merit zeitgeist. If you're out of food, the Panaceum Factory from the Reason zeitgeist will provide it and is also built on industrial districts.

I read somewhere that the metropolis ambition is easier than the prosperous future ambition (and colonize will nullify this achievement), so I chose to do that one. While I have yet to do prosperous future, I don't think metropolis is actually easier, or at least not in the context of this achievement. Even with every max pop growth law, it will still take a significant amount of time to get 50k without exploring (the max amount of pop I could get from a census is 3500, and the fastest I could get it felt like every 30 minutes or so). Incubation houses help but significantly add to your heat. And don't forget your housing and food requirements go up every census. All of that combined, and I think the total resource expenditure will far exceed the 100k each in prosperous future.