The Peklo (Hell) NNM lies in the Liberecký kraj – Liberec Region, between the village of Zahrádky and the town of Česká Lípa, in the canyon-like valley of the Robečský potok stream. The monument covers an area of 43.73 ha. at elevations of 247-303 metres above sea level. The area is currently protected on the basis of a declaration by the Ministry of Culture from 1987. However, the territory had been protected as a private reserve since 1895. The subjects of the protection are the stream valley, which is deeply incised into the block sandstones, and the rich population of spring snowflakes (Leucojum vernum) which grow here.
A large number of geomorphological landforms can be found in the valley of the Robečský potok stream with its steep, rocky walls, including rock overhangs, isolated sandstone blocks, narrow gulleys falling into the main valley, several small caves, ferruginous encrustations, pitted surfaces, imperfect mushroom rocks and other formations. The large number of pseudokarstic karren and the rock faces with right-angled and horizontal joints, which have been widened by weathering and erosion, are unique features at Peklo. The valley floor is covered with fluvial sediments.
The majority of the relatively wide stream alluvial plain is covered by communities with the dominant alder (Alnus glutinosa), with significant numbers of ash trees (Fraxinus excelsior) in places. In the spring we can also see the rich growths of flowering spring snowflakes (Leucojum vernum). Other significant plants which grow in these localities are lords and ladies (Arum maculatum) and bog arum (Calla palustris). The canyon slopes are predominantly covered with talus and ravine forest communities with beech (Fagus sylvatica), sycamore (Acer pseudoplatanus) and small-leaved lime (Tilia cordata). Spruce stands of cultural origin can also be found in the protected area. The edges of the canyon and the upper slopes play host to relict pinewoods , with an admix of silver birch (Betula pendula), Norway spruce (Picea abies) and sessile oak (Quercus petraea).
A total of 78 bird species, 18 mammal species, 13 fish species, 2 reptile species and 2 amphibian species have been recorded at Peklo NNM. Nesting birds include the eagle owl (Bubo bubo), kingfisher (Alcedo atthis) and dipper (Cinclus cinclus). Otters (Lutra lutra) have been observed in the Hell valley. The territory is also the home of significant gastropod communities.