How to Explore a Submerged City Without Drowning

Set Up a Base of Operations

Submerged cities are the largest structures in the mod and can take a long time to explore, so do not attempt them on a single breath. Build a small air pocket base nearby: a sealed room with a door, a bed, a chest for loot, and a source of Water Breathing. A Conduit placed here gives you a permanent safe zone to retreat to, restores breathing, and damages hostile aquatic mobs that follow you in.

Methodical Exploration

Enter the city and work room by room, placing torches or glowstone so you can find your way back. Seal doorways behind you with blocks to stop drowned variants from trailing you. Keep a stack of empty buckets to clear water from sealed rooms and create air pockets where you can pause. Note that cities contain hidden treasures — check behind walls, under stairs, and inside collapsed sections. Bring a bed and set your spawn at your base so a death does not send you back to the surface. If you find a room you cannot clear, mark it and come back with better gear rather than dying for it.