The Padirac Chasm opens as a hole in a field near Gramat, in the Lot, and it is 103 metres deep and about 33 metres across. You go down 75 metres by lift or staircase before the cave system even begins.
What is down there is a river. The Padirac runs underground for about 16 km before emerging into the Dordogne at the Montvalent Cirque, and part of it is navigable by boat, which is how visitors see the cave. It has been called one of the most extraordinary natural phenomena of the Massif Central.
The chasm itself is a collapse: at some undetermined point the roof of a large internal cavern fell in and left the shaft. The cavern is known to have existed in the third century, and people lived in it during the fifteenth and sixteenth centuries, when potassium nitrate was dug out of the area for gunpowder.
The first tourists went down on 1 November 1898, and the site was formally opened on 10 April 1899 by Georges Leygues, later the 87th prime minister of France. The lift and stairs arrangement dates from the 1930s.
The restraint is worth noting. The system runs to more than 40 km of galleries and only about 2 km has ever been opened to visitors. What is shown is a fraction of what is known, and what is known is presumably a fraction of what is there.
It is the most visited underground site in France, so book ahead, and the boat section means the tour is weather and water dependent.
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