It's there because Grug likes to cook and finds interesting ingredients growing underground. The rest of the dungeon's denizens go there because it's better than eating each other, though they'll occasionally do that anyway because Grug has to sleep sometime. The only reason they haven't killed him for his temerity is because he refuses to share the recipe for his Cheesy Mushroom &amp; Noodle Soup and losing it would make the head honcho of the dungeon very unhappy.