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 (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.

When the battle is over a save point appears, so take the opportunity to save.

Now it's time to tackle the six mage-like characters running around inside the cells. You can avoid fighting more than one in succession in the southern cell by starting a battle by checking a mage through the bars. In other words, stay out of the cell but face toward it and check a mage as he walks by. Otherwise one or both of the other mages in the cell may attack right after you're done with the first battle, leaving you no time to save, recuperate, etc. For the northern cell, it doesn't seem possible with out opening the door. These bosses are optional but you'll need to fight them to get the treasure chests they're guarding. These contain Dancer specific armor.

Now go to the cell in the northeast corner. Check the door or the bars and a new monster will break out and attack.

After the battle, go back to the northeast corner. A girl who was imprisoned there gives you a big kiss in gratitude for releasing her, then disappears through a back stair. (Suspiciously, the stair she uses was there the whole time.)

Follow her; the stair leads outside where you follow a path into a side building and up to the roof. Go to the west side of the roof and follow a similar path down back to the dungeon. Here you can finally reach the last treasure there.