The gorge of Erma river (the second name - Trun gorge) is located near the town of Tran and is recognized as one of the most beautiful sights of nature in this region of the country. Gorge to a depth of nearly 100 m and a width at its narrowest part to 5 m High (150-200 m) cliffs surround the river on both sides.

Special eco trail, originating in the southern part of the canyon, paved for hikers and nature lovers. The route is 13 km long, runs along the wooden bridges across the river Erma, and through a tunnel in the rock, then down the long wooden bridge is 35 meters, and then begins the ascent to the rock, located in the West valley. The most interesting objects of this route – the gorges of the rivers Erma and Jablanica. The view from this place is amazing for its impressive rock formations in the canyons of the rivers, picturesque frothy waterfalls and rapids. The gorge of Erma river was formed by the erosive effects of the river, for thousands of years it has cut through the limestone. Over one hundred years ago, the great writer of Bulgaria Aleko Konstantinov visited this place, which so impressed him that he exclaimed: "What, Switzerland? ".

This gorge declared a site of nature official order from July 1961 to preserve the unique rock formations. In addition, there is the amazing beauty of wildlife. In a small area there are about a dozen species of shrubs, trees and grasses. Some species are incredibly beautiful, such as lilacs, flowering in may or September and October smoke tree, and, of course, unique iris of Reichenbach, which is found only on the Balkan Peninsula, to see him in June.

Also impressive diversity of bird species: it is home to such interesting species like white stork, honey Buzzard, Montagu's Harrier, etc. Of mammals is possible to observe otters, small and large Tulip-like horseshoe bats, wolves, lynxes, etc. are Found here and amphibians: Triton Karelina, yellow-bellied snake, etc.