The Škocjan Caves are one of the largest underground river canyons on Earth, in the Kras region of southwestern Slovenia near Divača, where the Reka river vanishes at the foot of a cliff and thunders through halls up to 146 metres high, crossed on a slender bridge 45 metres above the water. This is the karst that gave the landscape type its name, a plateau of limestone where rivers disappear, and the Reka goes under here after collapsing two great sinkholes at the edge of the village of Škocjan, dolines with sheer walls where the river runs in the open air before it enters the mountain; the tour begins in the silent part, dripstone halls hung with stalactites and rising stalagmites built drip by drip over hundreds of thousands of years, and then the sound of the river arrives, and the path comes out into the Murmuring Cave, a canyon of black rock with the Reka roaring at the bottom, and crosses it on the Cerkvenik Bridge with the walls climbing into the dark above the lamps. The galleries along the canyon walls are not natural ledges but ten kilometres of path cut by hand by the cave explorers of the Austrian era in the nineteenth century.
Past the bridge the canyon opens into a hall where the river slides by almost silently in a pool, and daylight dropping through a chimney in the rock lays a green sheen across the water. For a long time no one could prove where the sunken river went; dye traced it to the springs of the Timavo, which surface near the Adriatic in Italy, 34 kilometres away and nearly forty hours later. In the flooded dark lives the olm, a blind salamander so pale and pink that people of the karst once took the creatures, washed out by floods, for baby dragons. A second trail follows the Reka along the bottom of the collapsed dolines in the open air, between the limestone walls. Škocjan is a river that goes into a mountain, and the bridge is where it is heard.