These remarkable caving pictures show thrill-seeker Dave Bunnell descending into Mexico’s El Sotano de las Golondrinas – aka the Basement of Swallows.
It is so deep that clouds form inside of it and measuring in at a staggering 1,200ft, it is one of the most dramatic free fall pits in the world.
The 61-year-old told Caters News Agency: "It's such a different world it sometimes seems like being on another planet.
Mexico’s El Sotano de las Golondrinas – aka the Basement of Swallows is so deep it has clouds inside it
“So the otherworldliness of it, and that you never know what may lay around the next corner, when exploring a new cave, even a small one can give you these feelings like no other."
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The pit was first descended in December of 1967 by a trio of Americans and since then cavers from all over the world have visited it.
It’s total depth is 1,638ft with the final few hundred feet accessible via a pit series called The Crevice.
The cave was first descended in 1967