This is an environment guaranteed to freak out even the most hardened player. A dungeon where most rooms are between knee and shoulder-deep in murky water.
- Your next step may be your last. The variable depth means that one misstep can plunge a heavily armoured character under water.
- Footloose. If the dungeon has been submerged for a while the stone beneath the character’s feet could be very slippery.
- Underwater obstacles. All sorts of debris could be under the murky water. If you are lucky you just stub your toe…
- Denizens of the deep. There are many monsters that like underwater dungeons; predatory fish & eels (inc. electric), cave-crocodiles, water snakes (inc. constrictors), tentacled horrors, the watcher in the water, jellies and jellyfish, water elementals etc.
- Strong currents. Literally sweeping characters away and battering them against stone walls and other unyielding objects. Or carrying floating objects towards the characters at dangerous speed.
- Who needs to breathe? Undead don’t. They may be perfectly at home under the water.
- Who the hell wastes skill ranks on swimming? Ever tried to swim in chainmail armour?
- Wooden furniture, daises, floors, balconies, stairs and walkways may be saturated and rotten. Thus they are likely to give way at any moment. The same goes for anything made of rope, like bridges and ladders.
- Saturated clothing and water-filled backpacks are very heavy. They also cause fatigue through making every step an effort..
Making it so much worse…
- Make it a winter dungeon where the water has frozen. You then have the fun of fragile ice, the cold, many rooms being very short because of the distance between the frozen water level and the roof, using fire spells etc. Think hypothermia…
- Adding slicks of highly inflammable oil on top of the water, or pockets of inflammable or noxious gas. What are the characters using to provide light?
- Rotting corpses turning the water into a disease-ridden broth. Corpses can also emit noxious vapours.
- Highly salted water making characters very buoyant but which attacks their steel and iron weapons and armour, and makes their eyes sting.
- Have the dungeon start out as mostly dry, but heavy rains up above lead to the dungeon flooding from the entrance. To get out before it fills the characters must fight against the flow of water, or they must find another way up. This is the spelunkers’ nightmare scenario.
- Rafts, canoes and coracles could be used to move through the dungeon. All of these are vulnerable to attack.
- Water-breathing spells/devices. The water is murky and full of debris making visibility between poor and non-existent.
- Water-walking sounds great until you realise there may be a shrinking distance between the water level and the ceiling…