Temple of the Ocean King

From Zelda - Wiki on Neoseeker

The Temple of the Ocean king is a temple erected in ancient times before the great seas when a people worshipped a god called the ocean King. But hundreds of years after the temple was built, it became cursed, and an evil monster was set in place in the bottom with great treasures strewn about. The significance of this temple is huge as you enter numerous times throughout the game to find clues to where to go next. But the trick is, since the temple is cursed, it sucks the life out of you unless you are in certain safe zones placed around each floor of the temple. You must use an item called the phantom hourglass to give you just a few extra minutes in there to search so you wont succumb to the effects of the temple. At the bottom of this temple is Bellum, the final boss of the game and the key to freeing Petra.