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 49 by 62 m wide and is undercut around all its perimeter, further widening to a room approximately 303 by 135 meters (994 by 442 ft) wide.