The belly of the beast is a fantastic location inside a large fictional creature (commonly a leviathan) that acts like a partially flooded cavern chamber. There may be lakes of acidic bile at these locations. There may be ruins, shipwrecks, shipwreck towns, boneyards, and other elements. In narratives, characters may be swallowed by a beast and must then find a means of escape. Bellies of the beast are home to swallowed sailors, pirates, and internal parasites.

Consider the internal anatomy of the beast. These spaces may lead up to blowholes, up to the throat and mouth, or elsewhere. Some animals may have multiple stomachs. If the beast is a artificial leviathan or behemoth (fashioned either by magic, clockwork, or advanced technology), its’ innards may contain rooms more similar to a building or vessel than a creature.