Basicly it's a huge worm with tons of different kinds of monsters inside and to get out you have to fight your way to it's heart and kill it. Boss monster? (Could be bigger than in the picture, btw) Done with MSPaint!! EDIT: Depending on its size, it could work either as a dungeon with weird monsters inside OR a sort of biome with different kinds of plants and creatures inside, maybe even with a sentient race inside that would help get you out of the worm if you decide not to destroy its heart. Killing or not killing the worm could result in different kinds of consequences: If you kill it, all the life from the worms corpse would spread around the planet, pretty much terraforming it into a habitable planet. The possible sentient race inside might however become hostile! If you don't kill it, you could find a way to visit the people in the worm once in a while to trade with them and find flora and fauna unlike any other inside the worm.
