Underwater Dungeon is a War Mode dungeon similar to the the ocean that spawns after Wall of Steel have been defeated. It is usually beneath the dungeon or near the ocean biome. The dungeon is filled with water like the ocean and has a Atlantic Temple at the bottom of the dungeon.
- Blue Merfolks
- Fishron's Servants
- Mermaids (or Mermans)
- Temple Guards (Atlas Temple)
Atlantic Temple is a building similar to the Jungle Temple (aka Lihzahrd Temple) and has a Atlantis chest inside which always contains a Supicious Looking Shell and some other miscellaneous Items. There's no water inside the temple so you have some time to breathe.
- The Mermaids spawn when your gender is male and Mermans spawn when your gender is female.
- The Merfolk families may drop Neptune's Shell.
- Mermaids (or Merman) might drop Supicious Looking Shell with a chance of 0.1%.