This is the Cave of Swallows, an enormous pit cave in Mexico. With a 370m drop from the cave entrance to the floor it has the largest cave shaft in the world. It could pretty much swallow up a whole skyscraper with ease. Like most pit caves and sink holes it was formed by centuries of carbonic acid in rain water chomping through the calcium carbonate that makes up limestone. It’s the same process that formed our favourite blue hole in Belize. It’s seems that people like jumping into holes no matter what the medium involved. This footage of base-jumpers flinging themselves into the abyss is totally mesmerising. It’s shot at the Cave of Swallows and nicked from the BBC planet earth series – enjoy.