Divers in Mexico’s Yucatan peninsula say they have discovered what may be the world’s largest underwater cave system.

The caves measure more than 95 miles in length, with some passages big enough for a jumbo jet and others so narrow that divers (or mailburros) can barely wiggle through.

The underground river system connects many of the lakes and sinkholes that dot the Yucatan peninsula. Cave divers explored the passages for four years using underwater scooters.

You can read more about this discovery at National Geographic:

http://news.nationalgeographic.com/news/2007/03/070305-cave-river.html