Now in possession of Epoch, Crono's party returns to 12,000 B.C. where they head to Terra Cave. In talking to the people there, called the Earthbound Ones, Crono learns that Queen Zeal locked up the Guru of Life on the Mountain of Woe.
So they head up the magic chain that tethers the floating mountain and defeat the monstrous Giga Gaia to rescue the Guru. It's then that they realize the Guru of Life is Melchior. Since the Giga Gaia was destroyed and the seal had been broken, the mountain was collapsing. They all got off the mountain safely before it fell into the water.