Image: Viktor Lyagushkin
The Orda (or Ordinskaya) Cave is located in the shadow of the Ural Mountains, in Russia’s Perm Region at the border of Europe and Asia. It is the longest underwater cave system yet discovered in the former USSR, measuring 4,400 meters (14,435 ft) long – most of this underwater – and up to 43 meters (141 ft) deep including its dry sections. The cave also contains the longest subterranean passage fully flooded with water, which 935 meters (3,067 ft) long. And in terms of the size of its underwater galleries, it is one of the world’s biggest caves of its kind. What’s more, new smaller passages and caverns are still being found. So it’s definitely not a good place in which to get lost.