Our second stop is the largest known cave shaft (vertical rather than horizontal cave) in the world. This cave is located in San Lois Potosi, Mexico. Known as the "Basement of Swallows" (Sotano de las Golondrinas) in Spanish, the cave is deep enough that it could fit the Eiffel Tower inside of it. It's depth reaches approximately 370 meters measured from the high edge, but can reach as low as 519 meters with its floor pits included.
The cave got its name from the many birds that live in holes and crevices in the rock walls. Most of the birds are actually green parakeets and white-collared swifts, and swallows are rarely found here despite the name. In the evenings, large circles of these birds exit the entrance and circle around it before free-falling back in to the height of their nests. Temperatures in the cave are quite low. Lots of vegetation grows around the entrance, while the bottom is covered in debris and guano.
The Cave of Swallows has become a very popular destination for BASE jumpers. A person without a parachute would take about 10 seconds to reach the bottom of the cave from it's mouth. Using a winch, BASE jumpers are able to get back out in approximately 10 minutes.