Note that Small Nether Dungeons are an opt-in feature. They must be manually enabled in the mod's config.
Small dungeon in an open cavern
Improved vanilla dungeons
An old, forgotten study tucked away in the corner of a Fortress
Fortress of the Undead
Catacombs surface entrance
Spider Caves nesting room
The Catacombs Floor B1
The Catacombs Floor 0