Ali Sadr Cave

Ali Sadr is a water cave, and that is the whole character of it. You do not walk through this one. It is one of the largest underground water complexes in the world, a network of canals, lakes and flooded passages running for kilometres, and visitors are taken through it by boat.

It lies at Ali Sadr in Kabudarahang County, about 100 km north of Hamadan in western Iran. The original name was Ali Saadr or Ali Sard, meaning cold.

In the summer of 2001 a joint German and British expedition surveyed it and put the length at 11.44 km. Iran's Cultural Heritage, Handicrafts and Tourism Organization has nominated it as a World Heritage Site, and their submission makes a specific claim worth quoting the sense of: that with about 2,400 metres of cave boating, it is the biggest cave in the world in that respect. They describe too many water halls to count, and a wide variety of stalactites, stalagmites and karst deposits.

The water is extremely hard, loaded with lime from the rock it has passed through, and it is not drinkable.

That hardness is not a flaw but the mechanism. Water that dissolves that much limestone on the way in is the same water that deposits it again as formations, and a cave this size in this rock is the long-run result of exactly that exchange.

Conditions inside are unusually stable. The water runs 0.5 to 14 metres deep at an almost neutral pH and a constant 12 degrees Celsius all year, and the only living thing in it is Nifargus, a tiny crustacean.

People have known this cave for a very long time. Excavation has turned up artworks, jugs and pitchers dating back 12,000 years, and the walls and passages near the exit carry images of animals, hunting scenes, and bows and arrows, which suggests mesolithic people lived here. It was still known in the reign of Darius I, between 521 and 485 BC, confirmed by an old inscription at the entrance to the tunnel.

Then it was lost. The knowledge of the cave disappeared entirely, and it was not rediscovered until 1963, by Iranian mountaineers.