The Podtrosecká Údolí comprises several little valleys that form an arch to the north and northeast around Trosky Castle.
At the bottom of canyon-like valleys whose parts are lined with rocks, there is a group of ponds and numerous characteristic localities with wetland and wet meadows, habitats of abundant vegetation and animals. Therefore, the locality was declared a national preserve (in 1999). Besides the Hruboskalsko and the Příhrazské Skály, it is the largest preserve in the PLA Český Ráj. It was declared a preserve in order to protect the wetlands on the bottom of the valley around the Želejovský Potok and the Žehrovka.