Romanian sewer workers accidentally discovered a cave which was sealed for 5.5 million years. Movile Cave is filled with evolutionary distinct exotic creatures (albino crabs, worms) which feed off sulfur-producing bacteria. Here are more details about the ecosystem and insects.
Cave systems were recently discovered beneath Antarctica which are warm enough to wear t-shirts in, and in which it is said a “lost world” of new animals and plants may exist.
A one of a kind sulfur based ecosystem exists in a Romanian cave completely sealed off from the rest of the world.