When you're done with Tokkul and the Village of the Ancients, jump back in your craft and head towards the jutting peninsula at the northwest corner of the enclosed body of water. Depart your ship near the castle you come across - this castle, called Castle Argus, is chock full of Gil and other items that'll be quite useful on your quest. Start by going through into the second room of the castle, where four candles adorn the walls. Hit the rightmost candle of the four to create a secret opening that'll lead you to a series of treasure chests. Within, a total of 9,200 Gil awaits. Proceeding further into the castle from this route, two yellow (and hence sealed) doors will be found. You can use a thief in your party to unlock the two doors. In the room to the left, a Killer Bow, as well as a Light Arrow and a Medusa Arrow can be found in a secret room to the right (hit the bookshelf to open it). In the room to the right, a Book of Light, Fire Arrow, Book of Fire, Book of Ice, Scholar Robe, and Ice Arrow can be found in treasure chests. Otherwise, there's little else to do here.