This place is a huge treasure trove. The items you’ll find will greatly augment your already-impressive collection, and if you need more money to purchase what you need, you’ll find a grand total of 7,700 Gil here!
Enter the castle. In the room with the four lit candles on a wall and a table in the western corner, zoom in and examine the far right candle with the sparkle to open a passageway.
Go along it to reach some treasure chests past the southeastern wall, each having 1,000 Gil within. Go up the stairs nearby.
Here, you’ll find six more chests, altogether containing 4,700 Gil . Open them up and continue on upstairs to the castle’s roof.
Go west and north. Go into the northwestern door now. In order to enter, put a Thief as the lead member of the party to pick the lock.
Within, examine the dresser to open up another room: go inside to find three chests. These contain a Killer Bow , Light Arrows , and Medusa Arrows .
Go back outside and go east to another doorway. Open it up as before and you will find another treasure room, as before. You’ll find the Books of Ice , Fire , and Light ; Fire Arrows and Ice Arrows ; and a Scholar Room . Backtrack to the room with the four candles from before and go upstairs right there.
Notice how you came up the west staircase? Go around to the other side of the table and go south through the pillar to find a hidden staircase and two chests in the next area, containing a Bomb Fragment and an Antarctic Wind . Go east and through the wall between the chests to find an Arctic Wind .
Backtrack to the table room and exit it to the south. Outside, you can go west to find a KO-healing wellspring, and you’ll find an HP/MP-healing wellspring to the east. Heal up and leave; there’s nothing else to do here.