Wikipedia
Ernstberg
The Ernstberg (also Erresberg) southeast of Hinterweiler is, at , the highest of the west Eifel volcanoes and, after the Hohe Acht, the second highest mountain in the Eifel overall. Its summit consists of pyroclastic rocks (Schweißschlacken) that form a volcanic crater that is open towards the east. This is where the basalt masses flowed out, forming a semicircle on the eastern slope of the mountain.
In winter there are excellent winter sports conditions on the Ernstberg due to its height. Cut langlauf tracks, a toboggan slope and ski hire hut are available.
Somewhat below the summit is a cave that runs through to the other side of the mountain and which is a natural monument. The cave entrances are barred to prevent access.