A series of Unfortunate events: The Grim Grotto by Lemony Snicket.

Unless you are a slug, a sea anemone, or mildew, you probably prefer not to be damp. The Baudelaire siblings encounter an unpleasant amount of dampness as they descend into the depths of despair, underwater.
In fact, the horrors they encounter are too numerous to list, and you wouldn’t want me even to mention the worst of it, which includes mushrooms, a desperate search for something lost, a mechanical monster, a distressing message from a lost friend, and tap dancing.