To Sua Ocean Trench is a natural swimming hole located on the southern coast of Upolu Island in Samoa. The name "To Sua" means "big hole" in the Samoan language, and it is one of the most popular tourist attractions in Samoa.

The To Sua Ocean Trench is a natural wonder formed by a volcanic eruption, which created two giant holes in the ground filled with seawater. One of the holes is the To Sua Ocean Trench, which is about 30 meters deep and 18 meters in diameter. It is surrounded by lush greenery and a wooden staircase that leads down to the water.

The water in the To Sua Ocean Trench is crystal clear and filled with fish, making it a popular spot for swimming and snorkeling. Visitors can also relax on the small sandy beach or enjoy a picnic under the shade of the trees.

There is a small fee to enter the To Sua Ocean Trench, and visitors are required to wear life jackets while swimming in the trench. The site is open daily from 7:30am to 5:00pm, and it can get crowded during peak season, so it's best to arrive early in the morning.