The Plakánek Valley Nature Reserve was declared in 1990 and is located on the border of the districts of Mladá Boleslav and Jičín between the villages of Podkost, Vesec u Sobotky, Střehom and Dobšín. The subject of protection is a valley with sandstone rocky edges and towers, wetland meadows and fragments of floodplain communities, scree forests, relict rock pine and acidophilic and pine oak forests. In the distant past, the current habitats have replaced the original large ash-alder floodplain forests. The protected area is in the care of the AOPK ČR - regional office in Liberec.
The name Plakánek comes from 17. century, according to the Plakák family, who burned coal in this area and from that they had "weeping" eyes.
In the year 2015, the reservation was carelessly felled in the territory in violation of the prescribed procedure according to the management plan, which damaged the protected area.
The main valley, also called Střehomský Plakánek, was dug by the Klenice River, which is also fed by several springs rising from rocks and hillsides. In the southern part of the valley there is a pond called Obora or Pilský. Not far from the pond farther south to the main valley of Plakánek side valley called Vesecký Plakánek (sometimes also Small Plakánek), which formed the Vesecký stream, flowing by name from Vesec. In this rocky valley, several old quarries have been preserved, where quality sandstone was obtained for construction purposes. The northern end of the Střehomské Plakák is formed by Kost Castle and behind it the valley is called Prokopské and leads to Libošovice.
In the Plakánek Valley Nature Reserve there are many interesting and protected plant species such as: Iris pseudacorus, Silene dioica, Trollius europaeus, Dactylorhiza majalis, Lunaria rediviva or Spring Snowflake (Leucojum vernum). The only place in the Czech Republic is the glacial form of the red worm (Melandrium rubrum), which was first described in 1853 by the pharmacist WJ Sekyra from Mnichovo Hradiště.
Forests with dominating coniferous trees include the eagle owl (Bubo bubo), common kestrel (Falco tinnunculus), raven (Corvus corax), alpine newt (Triturus alpestris), grass snake (Natrix natrix) and frog (Rana dalmatina) . A critically endangered species of the Lesser Horseshoe Bat (Rhinolophus hipposideros) winters at Kost Castle.
Kost - The castle is hidden among the surrounding hills, was built in 14. century and was never conquered.
Studánka Roubenka - Well with clear water, favorite place of writer Fráňa Šrámek, who lived in Sobotka. Mention of the well appears in his poems.
Poráň - A place where the prehistoric fortified settlement from 7 was. - 5. century BC until 13. century. To the fort belonged a burial mound, which is located near the well Roubenka.
Vesec - Village with preserved village architecture and round village square. There is a sculpture of the Holy Trinity in the village.
Semtin linden - It is a memorable tree by the road between Sobotka and Podkostí. The lime tree was destroyed in a severe storm, but a new tree has already been planted near it.