Biome Chests

A Dungeon Chest can be opened with a Dungeon Key of the same color. They have a 1 in 4000 drop chance in their respective biomes, and can be found at any elevation inside those biomes. (e.g. Frost Key in Snow Biome).

The keys can drop from any mob inside of the biome once hardmode is active.

Loot
Besides the common items listed here they have the common items depending on the height they were found: Surface, Underground or Caverns. It can only contain the Scourge of the Corruptor in a Corrupt world and only the Vampire Knives in a Crimson world