#arguably

whoever built the trial chambers also built the nether fortress. they built the blazes and the breezes in a similar method. ive seen some people online say that the trial chambers could habe been built by pilligers, and i like that.

this also means they likely went to the end, as blaze powder is necessary to get to the end and theres an end portal room in woodland mansions.

igloos were also built by modern day pillagers (bc who ELSE would build them? they had to be built recently bc of the basement)

mineshafts were built by (or at the very least utilized by) the ancient city folks. they had a dual purpose: first to make mining natural resources in other layers easier, but more interesting as mini highways to facilitate trade between them and the surface, sending things like diamonds and riches up, and getting seeds and food sent down.

they probably traded with pillagers? pilligers seem to have a LOT of wool things.

ancient cities may have been built to escape the zombie apocalypse. until it got skulked. either that or they came through the giant portal, trying to (and failing) to escaping the skulk.

the dungeons (or monster spawn rooms, as called by the wiki) are tombs. by looking at the loot there, we can tell that the society of whoever buried their people this way valued horses, music, food (thats mostly gone bad now), riches (both in metals/ore and magic), and possibly trophies of combat.

jungle and desert temples may have also been originally built to be tombs. the loot seems to be pretty similar to the loot in dungeons, so likely the same or similar culture or religion. at least for dealing with the dead. id guess the people buried in these places were a lot richer though.

pilligers and villigers used to be one united people, but at some point they split. when? idk. anything i say was made by pilligers or anythijg done by pilligers may have been a joint effort. besides igloos for obvious reasons. trial chambers were probably also after the split though.

the tombs, ocean ruins, ocean monuments, and ancient cities may or may not have been built by the (p/v)illiger nation people. im leaning not.