Viewpoint Hohentwiel in Singen (Hohentwiel)

You're standing at the Hohentwiel, the home mountain of the town of Singen. Take a good look at its shape. It rises steep and alone out of the landscape, about 260 metres above the Aach valley. There's a reason for that. Some seven to eight million years ago, this was a volcano. What you're looking at now is the old volcanic pipe, filled with a hard rock called phonolite. Ice age glaciers scraped away the softer rock around it, and only that tough core was left standing.