Caves are some of the most interesting environments on Earth, with beautiful rock formations, unique animals, and a long and fascinating history.

While most people think about caves on land, there are also huge caves that are underwater. These caves often formed in the distant past, before they were flooded by changes in sea level.

One example of this is the Ox Bel Ha system, which is located below the water’s surface on Mexico’s Yucatan Peninsula. It happens to be the longest underwater cave system in the world, measuring in at over 524 kilometers, which is longer than the entire Grand Canyon system.

And divers are still finding new areas to explore, pushing its length even further.

This is just one of multiple underwater cave systems in the region, all of which are still being explored on a regular basis.

When first found, Ox Bel Ha didn’t seem that interesting. Cave explorer and diving instructor explained:

“From where it is most easily accessible, a side road, the cave is marked by a group of small, complex and unattractive tunnels. This alone was enough to turn away the less determined cave diver, especially since there were a number of highly decorated cave systems under active exploration at the time.”

It took two years after it was first discovered before anyone took the time to really swim in and explore the cave. Needless to say, once they got into it, they were shocked at just how large it was.

After the initial wave of exploration, it attained the title of the largest known underwater cave system in the world, measuring several hundred kilometers.

Then, the nearby Sistema Sac Actun system was in second place until 2018, when it was found that the Sac Actun and the Dos Ojos cave systems were actually linked, putting their total combined length at 346 kilometers, pushing Ox Bel Ha down to second place…for now.

It took until 2021, but at that point, enough new caves had been documented to push Ox Bel Ha back to the top of the list, and it just keeps going.

In 2023, that length took a big leap forward when a team of divers found a massive new area. They explain:

“we popped into a massive freshwater room with dark decorations and gray-colored sediment hills. To our surprise it looked like we were the first ones there.”

The addition of that segment of the cave system put the total length at just over 524 kilometers, solidifying it as the longest on Earth. At least for now.

If you thought that was interesting, you might like to read about 50 amazing finds on Google Earth.