The Kernberg basalt quarry between Rotava and Jindřichovice is now a 35 m deep lake, from which a cylindrical conduit wall of a Tertiary volcano protrudes along with basalt columns and pyroclasts that were ejected from the crater. The basalt hill originally towered 76 m above the surrounding landscape. Kernberg was the largest basalt quarry in the Czech Republic. It operated before 1785 until 1995.