Golden Sun: The Lost Age/Naribwe
When you first get here, use the Inn/Sanctum if you need to (there's no building for the Sanctum, it's just a healer guy in the upper-right of the town). Use Lash on the rope by the Inn, climb down the vined stump, and grab the Thorn Crown from the chest (this is best equipped to Felix). Outfit yourself with some new gear if you need it, then head on through the upper-left hut. Outside in the enclosure, use Whirlwind on the ivy covering the ladder, climb up, and use Reveal to find a chest containing a Unicorn Ring. Now, head into the top-right hut, the one with the animal skull above it.
In here, talk to the fortune-teller. Give him 20 coins, then when you get to choose what you give him, choose your Laughing Fungus that you got from Gondowan Cliffs. He'll do a little dance...
"Beyond this item, I see a path for you to follow...I see you inside a sacred icon. By listening to the voices, you will earn a precious item."
That's pretty much just told you what you're going to be doing - raiding a sacred idol of a tribal civilisation. Morals never really got going in this world, eh? Well, they stole the black orb of Piers' so you're going to be doing a little stealing of your own. When you're ready, head north out of Naribwe. Follow the path until you reach Kibombo Mountains.