Dunajec river - flow of Visla river from the right side. It creates a 17 km long state border from Slovakia with Poland. In the section between Červený Kláštor and Szczawnica Nižna Dunajec river cuts the Pieniny mountains through a deep gap valley with five dug meanders. By erosive activity Dunajec river created a deep enclosed gap valley with dropped and varied rocky figures on the slopes.

The gap was formed already in pliocene, this fact is testified by the erosive tablelands in the altitude 120 - 150 m above the valley. Kláštorná hora, Holica, Kače and Kyčera jet out above the gap, on the right side of Dunajec. On the Polish side of the gap the peak Tri Koruny (Three Crowns) dominated.

The Dunajec gap, one of the most beautiful gaps in Europe, is a state nature reserve (declared in 1967). It is the part of the Pieniny National Park and the most valuable territory of it from the viewpoint of natural science and landscape.