Pools of acid are only found inside the Worm.
Acid is not as dangerous as lava, as it is possible to swim through pools of acid for three seconds without taking any damage. However, the Spelunker will begin to take damage if they remain immersed in the acid for too long.
Pools of acid also produce bubbles at their surface, similar to those blown by a Snail. Touching these will immediately deal one point of damage.
Similar to pools of water and lava, destroying the walls will drain the liquid down to the level of the leak. Acid will not dissolve items like lava does, but deals constant damage to monsters.
Acid needs one free room to generate. Additionally, about halfway down, a wide acid pool always generates, where the Crysknife is located.