I keep having ideas for various kinds of ruins in this game, and messing around in creative and exploring a winter forest just gave me a ton of ideas.
For example, what about ruins of increasing tech and rarity? Obviously it could be a setting perhaps, but I was thinking of the medieval ruins being more common than the modern ones. Things like underground complexes or topside research stations or gas stations being overgrown and looking as if they've been left there for a very long time. They could also have good but rare loot, for example a gas station could have old tinned foods and drinks that have survived, or a topside research station could have some modern medicines worth a lot. It would also be nice to have to power some of them up when electricity comes out, or else you'll have to creep through an underground complex with your flashlight out, and who knows what's down there with you?
Those are just my ideas, if anyone else has any comment and share, I'd love to read them!