Into the belly the of the beast is an encounter or event in narrative or game worlds in which characters find themselves inside some great leviathan or behemoth. They may have been swallowed or they may have wandered in through a cavernous maw. The entrance, or mouth, may have closed behind them and adventurers may need to find an alternative exit or means to reopen the way out. Generally, the end goal of these encounters is to escape or to recover an item or previously swallowed person prior to escape.
When designing these encounters, the layout of the interior area is important. Consider the physical space, particularly the belly of the beast, which may be the primary area characters explore. This region may contain remnants of what has been swallowed before, including ruins, shipwrecks, boneyards, or other elements which can be explored. Lakes of acidic bile or acid spouts may act as terrain hazards. A slowly increasing level of stomach acid may force characters to action before it becomes too late.
If the beast is an artificial behemoth or leviathan, its’ internal spaces may more resemble rooms and the overall structure may more closely resemble the interior of either a building or a vehicle. The internal spaces may share characteristics of real organs – such as rooms with great pumps for hearts or steam-engines for lungs. If the creature was created magically, certain rooms, like the heart chamber, may be particularly important or central to the magic which keeps it operating.
Escape may require getting the creature to sneeze.
The great beast may have aggressive parasites (worms or other internal guests) which may be dangerously territorial.