The Felsenmeer in Hemer, Sauerland, is a forested geotope with a strongly fissured underground and numerous visible rock formations that dates back to the Tertiary period. The area of the rock sea covers about 35 hectares, is about 600 meters long, 200 meters wide, and lies 45 meters above the valley floor. It is divided into three subareas: the Great Rock Sea in the northwest, the Small Rock Sea in the south, and the Paradise in the southeast.

A legend holds that in the present-day area around the Sundwiger Forest, dwarves settled in ancient times. Under the rocks, they searched for gold, silver, precious stones, and other hidden jewels. The famous dwarf king Alberich was lord of all the treasures. When the neighboring giants heard about all the wealth, they set out to plunder the dwarves’ rock castle. The dwarves were able to hide from the giants in the furthest underground passages, while the giants could only reach the great rock hall. Suddenly Alberich cast a spell and the ceiling of the rock hall fell on the giants, creating the Felsenmeer located at this place. A tombstone of a giant can still be seen today: A rock slab with an effigy of the giant was placed in Paradise.

In 1962, the Felsenmeer was designated as a nature reserve because of its natural, geological, and cultural importance. Bridges, walkways, and an observation platform were built so that visitors can explore the area without wearing down the rocky terrain.