The Underwater Ruin (海底遺跡) is of unknown origin. It may be the ruins of an ancient civilization sunken deep beneath Moga Island. The Elder Dragon, Ceadeus, makes its home here along with Goldbeard Ceadeus and the Abyssal Lagiacrus. There is a shortcut from base camp to Areas 2 and 3 available when you have repelled Ceadeus. The battle soundtrack of Underwater Ruin is the same as the Tower's battle soundtrack. A Dragonator and two ballistae are found in these ruins,supposedly built by the old ancestors of moga village chief to keep monsters like Ceadeus at bay.