Archives are large underground dungeons - a great source of enchantments.
Archives are found underground in any biome a Trial Chambers can be found, between Y levels -20 and -40.
Archives are large maze-like structures filled with bookshelves, loot, and traps.
There is a guaranteed main room with a red carpet directly next to the Archive's library room. The library is the largest room in the Archives, filled with enemies and Chests of loot.
The Archives are full of Illusioners and Vindicators, but because of the Illusioners' magic, they're hidden, and will only appear when you come close.
Chests:
Guaranteed
1-3 Enchanted Books (Enchanted with XP level equivalent of 28)
Random Items (3-7 of these are found)
1 Woodland Explorer Map
1 Compass
1 Empty Map
1 Carved Pumpkin
1 Pumpkin
1 Goat Horn (regular variant)
1-3 Books
1-3 Hay Bales
2-5 Bottles o' Enchanting
2-7 Paper
3-6 Smoke Bombs