The Black Hole Trail in Slovenia.
The only underground MTB trail in the World!
Black Hole Trail is a mountain bike trail through abandoned tunnels of Lead and Zink Mine Mežica. Before the trail was built, a human has not set foot in these tunnels in over 25 years, ever since the mine shut down. The colossal chambers used to hold tonnes of lead which was mined in the past. The trail runs over five levels of the mine and descends a total of about 150 metres.