I was in Three points, when i saw that there was a house open that i'd never entered before. I was confused, and went inside.There was a small room with tunnel leading into a huge chamber! What is this room?
That sounds like the Teocalli of Sacred War, where you put the Tzolk'in Stones in the quest Count of Days, which requires you to collect said stones from all over Azteca. It's Azteca's "book quest" where you collect books etc. (or in this case, stones) with information about the world.
I quite enjoyed this method of exposition, like in Avalon. The previous book hunts made the Area's lore a bit hard to follow since the space in between finding the books too far in between, this way you have a more complete story in one hit...provided you're actually interested in the Zone's lore and history that is.