The Chocolate Quest mod for 1.6.4 is based off of the old better dungeons mod. It adds new dungeons to the game that are unique to each biome. In these dungeons you will find new mobs, bosses, and items.
Castles with dungeons in their basements. Spawn in plains.
Ice Plains Castles:
Similar to normal castles. Found in snowy biomes.
Spawn under snowy biomes.
Deep Jungle Caves:
Large caves full of vegetation. Spawn under jungle biomes.
Found under taiga biomes.
Spawn in mountains.
Spawn underground in every biome.