Cave of Swallows

The Cave of Swallows, also called the Cave of the Swallows (Spanish: Sótano de las Golondrinas), is an open-air pit cave in the municipality of Aquismón, San Luis Potosí, Mexico. The elliptical mouth, on a slope of karst, is 49 by 62 m (161 by 203 ft) wide and is undercut around all of its perimeter, widening to a room approximately 303 by 135 m (994 by 443 ft) wide. The floor of the cave is a 333 m (1, 093 ft) freefall drop from the lowest side of the opening, with a 370 m (1, 210 ft) drop from the highest side, making it the largest known cave shaft in the world, the second deepest pit in Mexico and perhaps the 11th deepest sheer drop in the world.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).