A mountain primeval forest on the south-west slope of mountain Boubín. It covers an area of 46,67 ha, the nature preserve as a whole measuring 666,41 ha. The forest growth consist mainly of spruce, beech and fir trees. Some trees are 300 to 400 years old. The primeval forest is a sample of unviolated Central European countryside. The King of the Boubín Spruces fell as a victim of the wind in 1970. It was 440 years old. The small lake called U Pralesa is an artificial reservoir from the 19th century. The beginnings of the primeval forest preserve date back to 1858.