The Underwhere is the seventh world in Super Paper Mario. The first time Mario came here was because Dimentio sent him there along with Peach and Bowser who were lost while being sent. Mario finds Luigi here so that Luigi can help him find a nimbi named Luvbi. The second time Mario came there was because there was a pure heart there. Mario soon finds Bowser here but Bowser fights him since Peach was lost after thinking Mario was just torturing him soon Bowser joins your team again to help find Peach. After you pass the three doorguys you move on to the Overthere.