National natural monument (NNM) – so-called “rock organ” situated near the village of Prácheň close to Kamenický Šenov. This rock formation consists of mostly vertical basalt columns (pentagonal or hexagonal in shape). In the 19th and 20th centuries, basalt columns were mined in the area. After the mining was discontinued, the mine pit was filled with rainwater to create a small lake, which is now a part of the NNM. The Panská skála rock has been a protected rock formation since 1895, which makes it the oldest geological preserve in the country. It is accessible for both hikers and cyclists.