The Great Blue Hole has a massive underwater sinkhole - Apparently.
The Great Blue Hole, located in the center of the Lighthouse Reef Atoll in Belize, is a massive underwater sinkhole that is approximately 300 meters (1,000 feet) in diameter and 125 meters (400 feet) deep. Formed during the last ice age, around 15,000 years ago, when the sea level was much lower, the sinkhole was once a dry cave system. Today, it is a popular destination for scuba divers and a natural wonder of the world, attracting visitors from around the globe.