The Great Blue Hole, located off the coast of Belize, is one of the world’s true natural wonders. Now we’re finally learning more about what’s inside this mysterious phenomenon: A high-profile mission of exploration featuring billionaire Richard Branson recently took a submarine down to its depths, creating a high resolution 3-D map.
On one level, everything you need to know about the Great Blue Hole is right there in the name. Circular in shape, the sinkhole is located at the center of Lighthouse Reef, an atoll in the Caribbean Sea. It’s around 300 meters (1,000 feet) across and 125 meters (400 feet) deep, and is easy to spot by how its deep blue color contrasts with the light blue waters surrounding it. Earth-observing scientists, like those at NASA, believe it to be the largest sinkhole of its kind.
Seen from above, a very light, greyish-white ring can be seen surrounding the Great Blue Hole. That ring is actually elevated coral, dried out by being too close to the ocean’s surface.
The mystery of this peculiar place has enticed explorers for decades. The Great Blue Hole first entered much of the public’s imagination in 1971, when it featured on an episode of The Undersea World of Jacques Cousteau. The famed French oceanographer filed there for an episode titled “ Secrets of the Sunken Caves.” Because that right—the hole is technically a vertical cave.