Right after Gobi joins you, head down south into the water from the area the party is stranded at.
First head east to the town of Prima (you'll know it when you see it). There is a volcano north of Prima that you are supposed to visit later on in the game. However, you can still access it and obtain its treasures. It is recommended you either level up Gobi quite a bit if you plan to venture and grab the treasures alone, for the monsters are pretty rough around here. You could however, wait until you get back together with your party and then head into the volcano; either way is fine. The most noteworthy item you can retrieve from the volcano is the SharpBW, one of Bo's two one-handed weapons. If you decide to raid the entire volcano, you should come up with: a SharpBW, PowerDR, 3000GP, 2000GP, M. Drop, and a Herb.