Orgnac sinkhole was discovered by Robert de Joly in 1935 and is located on the plateau of the same name. It is one of the region's most interesting places to visit. It would seem that an earthquake turned these underground caves upside down, during the tertiary era. The tour of the latter begins in the upper room, then you walk down to the deeper red rooms. You'll find the sinkhole's finest stalagmites in the upper room. They are shaped like «palm trees», «pine cones» or «stacked plates». Each shape depicts a geological phenomon. The next stage of the tour takes you to the Chaos Room. In this magical cave, you'll see concretions, stalactites and stalagmites. The visit ends via the red rooms. You'll be enchanted by the imposing calcite pillars in the first red room. Nearby, a tribute is paid to the sinkhole's explorer, Robert de Joly.