Within the forest on the Brasselsberg mountain of Kassel, Germany and between the Teufelsmauer and the Bismarckturm you need to pass a gate made of stone: the Porta Lapidaria. At least these are two rocks consisting of basalt originating from volcanic activity. One of the left-hand side of the path, one on the right-hand side. The rest is your imagination.
Brasselsberg / Habichtswald