50. Unending Fight
WARNING! WHAT YOU SEE BEFORE YOU IS THE FINAL SAVE POINT OF THE GAME! WARNING!
After you defeat the last boss, you'll be able to make Clear Game Save. When you load this particular save data, you'll be returned just to the point before entering Underwater Palace.
Save your game at SPN. If you need recovery items, return to 7th floor and restock at Genma's.
Walk W, open the door and go upstairs for some scenes of getting access to final... dungeon, so to speak.