Final Fantasy III/Hein Castle

Castle Argus treasure room
Check the fourth candle from left for a secret passage to the east. You will then come in a room with 3 chests (3000 Gil) behind a wall which can walked through. Go upstairs and you find 6 more chests (4700 Gil). Go upstairs again and go left until the door. Unlock it with a thief in your party, if you don't have one then change someone to a thief and place him at the top of the party.

Check the dresser to give way to 3 chests (Killer Bow, 20 Light Arrows and 20 Medusa Arrows). Exit the room and go right to another door. Unlock it and you are in a room with 6 chests (Book of Fire, Book of Light, Book of Ice, 20 Fire Arrows, 20 Ice Arrows and Scholar Robe)

Go back to the room with 4 candle and go upstairs.

Now you're done here so exit the castle and go southwest to a forest called...

Living Woods
You will meet some fairies there and a crater where the elder tree was. The fairies tell you that Wizard Hein from Castle Argus came and placed a curse on the elder tree and took him. The elder tree is transformed in a castle and wander the desert near Tokkul aimlessly. They also tell you something about Hein's weakness. Now go back to the town of Tokkul.