Ravne: A Story About Stones
Ravne underground tunnel labyrinth in Visoko, Bosnia and Herzegovina, has been dated as Europe's oldest prehistoric tunnel network, where human presence endured for over 30,000 years. A date of up to 40,000 B.C.E. has been suggested by carbon dating of organic material found in the tunnel network.

In contrast to ancient mining tunnels, Ravne underground tunnel does not show traces of ore extraction. Moreover, it is possible to breathe freely anywhere inside the tunnel labyrinth without auxiliary respiratory support, while ancient (and modern) ore mines need a source of external oxygen.
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