Radotínské údolí, Nature reserve in Ořech and Radotín, Czech Republic.

Radotínské údolí is a nature reserve of 130.24 hectares on the southwestern edge of Prague, at 250–350 m above sea level, stretching along both banks of the Radotínský potok and around the left bank of the Mlýnský potok. It lies in the cadastral areas of Zadní Kopanina and Kosoř, bordered by Zadní Kopanina to the north and Kosoř to the south, with the Cikánka settlement to the east. Devonian limestone slopes carry steppe and forest-steppe communities.

The area was first declared a nature reserve on 7 June 1950 by the Ministry of Education, Sciences and Arts, with consent from owners including České cementárny a vápenky. It was re-declared a state nature reserve on 17 September 1975 by the Ministry of Culture of the Czechoslovak Socialist Republic to protect steppe and forest-steppe communities on Devonian limestone.

The valley is called the valley of beautiful mills: water power once drove twenty-two mills on the Radotínský potok, grinding grain from the fertile fields. The mills are still inhabited but no longer mill. The best preserved is Zadní Mašek, also called Dolejší kopaninský, Urbanův or Kozákův, near the confluence with the Mlýnský potok.

The reserve is open for hiking and nature observation, with a protection zone extending roughly 50 meters beyond the marked boundaries. Visitors should wear suitable footwear for uneven terrain and be prepared for changing weather conditions.

The valley is one of the most important sites in the eastern part of the Prague Basin, where Joachim Barrande conducted geological research. It also supports one of only nine populations of the Austrian dragonhead in the Czech Republic.