Castle in the Clouds

After saving Ketonia, go to Diamond Lake and listen to the voice. It willl tell you to try places formerly not available to you. This place is Cross Island, and you'll have to locate that for yourselves! It's not hard to find it… 

From Cross Island you will be teleported to a place in the mountains. Just walk up to the village there and let the man take you to the maze leading to Castle in the Clouds.

When you arrive in the maze, there are a few locations of interest.

At X: 84 Y: 5 there's a party of dead adventurers with some items still intact.

At X: 84 Y: 80 you might find a necklace.

At X: 86 Y: 75 is a map on a dead elf showing the way to the castle.

At X: 64 Y: 75 there's a sword. It's cursed.

There are in fact TWO castles in the maze. The first is located at X: 6 Y: 8. It is the castle of a bad guy and you'll have one MAJOR battle coming your way if you enter it.

The castle of Zukar is located at X: 5 Y: 87.