Sotano de las Golondrinas

Sotano de las Golondrinas, the "Cave of Swallows," is a vertical karst shaft in the Huasteca Potosina region of San Luis Potosi state, Mexico, dropping in one uninterrupted freefall pitch of roughly 330 to 370 meters from its surface opening to the rubble slope at its base, ranking among the deepest known cave shafts of its kind in the world. It formed by the dissolution and collapse of limestone bedrock along vertical joints, leaving an opening at the surface that is relatively modest in diameter for a shaft of such depth, so much of its lower chamber flares out into a much larger underground space than the entrance suggests. The cave earns its name from the thousands of white-collared swifts and green parakeets that nest on ledges within the shaft and pour out of the opening at dawn in a dense, swirling column, a spectacle that draws both birdwatchers and BASE jumpers, for whom the shaft is one of the few places in the world offering a legal, sustained freefall of this length into a natural cave. This entity documents Sotano de las Golondrinas specifically as a geological formation, one of the world's deepest single-drop karst cave shafts, formed by limestone dissolution in the Huasteca Potosina.