via youtube.com
"The Cave of Swallows, also called 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 160 by 205 feet wide and is undercut around all its perimeter, further widening to a room approximately 995 feet by 440 feet ) wide. The floor of the cave is a 1,094-foot freefall drop from the lowest side of the opening, with a 1,220-footdrop 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 in the world."
