Gaia Rock
From Golden Sun - Wiki on Neoseeker
Gaia Rock is located north of Lemuria, and is the location of the tablet that gives you the psynergy Sand. It is also the home of the truly fearsome boss, the Serpent. Gaia Rock, as it's name suggests is based solely around the Venus element. During this entire dungeon you must scale the mountain on the outside first then on the inside. The only way to advance inside the mountain is to get to the top of the mountain and get the Dancing Doll that will move the dragon statues inside the mountain.
You'll eventually find out that the lights you activate inside the mountain help you weaken the Serpent as it's invincible when you try to confront it head on without having at least 3 lights on. The Serpent, as said is the big boss of the dungeon and very difficult to defeat. There are strategies on how to defeat the Serpent.
