Demetrios1453
Legend
That was in Pools of Darkness, where you could visit all sorts of locations on/in Moander, although only the heart was a fully developed dungeon.I remember one of the old SSI/TSR video games had the party go through the comatose body of Moander - basically a giant, godlike shambling mound. If you waited too long, every certain amount of rounds, the heart would pulse and it would push you into rooms. I could see mapping that in a very generic, abstract way - come in through a giant wound on the 'leg' and try to get to the brain.
There is also the 1991 module Nightmare Keep, which has a huge underground labyrinth that the characters will only slowly figure out is within the body of a giant creature.