National natural reserve SOOS is a unique natural reserve north of Františkovy Lázně, larger part of it occupying the area of Skalná. The national reserve was established in 1964 and its area occupies 221 ha. The word „Soos“ means swamp in the Egerland dialect. 1,2 km long nature trail leads through the bottom of a dry salt lake on wooden pavements. The bottom of the dry lake contains shells of lake weed that gave birth to the unique diatomeus shield. The lake today is a peat-bog and mineral moor, echoing the former volcanic activity through the so-called „mofets“ – mud volcanos bubbling with CO2. It is also a place where mineal springs rise, i.e. the Emperor´s spring. Because of late volcanic activity, the peat and other factors the area has an extraordinary look which is diffucult to describe but is certainly worth seeing. A place like this in not found elsewhere in central Europe.