Final Fantasy V/N-zone II

N-zone (floating castle)
This section seems to be made of ledges floating in the air. Have a Thief or equip a character with the Secret ability to see the paths between the ledges, but even without this it shouldn't be too hard to find your way around. Follow the ledges west and exit in the northwest corner to the castle proper.

N-zone (X-death's castle)
Enter the castle and explore the main floor. There is a stair up in the center of the room but it leads to a locked door. To the east and west are to passages, each with a door north and a door south. The south doors lead back outside where you can enter small towers with treasure. The north doors lead to empty rooms but they do show you stairways as a hint for further exploration. Behind the stair up there is a stair down, follow it to the castle dungeon.

There are cells here with what appear to be prisoners. Don't be fooled though, these are boss monsters. Start with the cell in the southwest corner. This boss is technically optional, but since you will definitely want the save point he is guarding it's pretty much a requirement.