Rehimido is the main story dungeon in Elona+, similar to Lesimas in the normal game. To enter, you must clear the Chaos Shrine, the Machinery Fort, and the Valley of Hereafter. Locations of the dungeons are detailed in the South Tyris page, or in their individual pages. After this, you can talk to doctor to receive the Card key quest item. This will let you enter the dungeon. If you try earlier, you will wind up on a regular forest map. In addition, it requires you to leave at certain points to be able to continue. For more details, check the Main Quest (Elona+) page. It has 30 floors in all. Also similar to Lesimas, you can warp back to the deepest floor you have been to.