A Canyon Carved in Darkness
Deep beneath Slovenia's Karst plateau, the Reka River has carved one of the world's largest known underground river canyons. This immense subterranean feature is the center of the Škocjan Caves, a UNESCO World Heritage site recognized for its exceptional geological phenomena. The river flows on the surface for about 50 kilometers before it reaches the limestone bedrock and disappears underground. Here, it has sculpted a passage that is 3.5 kilometers long, up to 60 meters wide, and reaches heights of over 140 meters.
The canyon's largest chamber, Martel's Chamber, is one of the biggest in Europe, with a volume of 2.2 million cubic meters. Its highest point is 146 meters above the riverbed. The entire cave system, formed in Cretaceous and Paleocene limestone, has an explored length of 6.2 kilometers. After heavy rains, the volume of water entering the caves can be immense, causing the river level inside to rise by more than 100 meters. After traveling 34 kilometers underground, the river resurfaces in Italy as the Timavo River. Above ground, the landscape is marked by enormous collapsed dolines—Velika Dolina and Mala Dolina—which are collapsed sections of the former cave ceiling where the river plunges into the earth.