Sprinkled across the ocean floor, invisible from the surface, are hundreds—possibly thousands—of sinkholes known as blue holes. They are as intriguing to scientists as black holes are to astronomers, and there is still much to learn about them.

One blue hole that has recently captured significant attention is called the Green Banana, located offshore from St. Petersburg, Florida. Scientists are preparing to venture into this sinkhole, which extends roughly 275 feet deep and resembles an inverted, hourglass-shaped, 20-story building anchored in the ocean floor.

Scientists are preparing to venture into the "Green Banana" sinkhole.

As one of the deepest blue holes ever discovered, the Green Banana will be the subject of the most comprehensive study conducted to date. Researchers are working to determine whether it connects to other sinkholes and whether freshwater flows within it. Because of its depth, scientists are eager to see what it may reveal about life in the deep ocean.

Due to their unusual seawater chemistry, blue holes are typically teeming with life and are often remarkably clear. However, their narrow entry points prevent automated submersibles from entering, which is one of the main reasons so little is known about them.

During the upcoming mission, divers will enter the Green Banana using a 600-pound, triangular-shaped lander. What they will discover—both biologically and chemically—remains unknown, but the exploration promises to shed new light on one of the ocean’s most mysterious environments.