Hohentwiel

The Hohentwiel is a phonolite plug, the solidified throat of a Miocene volcano, standing about two hundred and sixty metres above the Hegau plain with a further ring of similar cones around it. Fortifications grew on it from the tenth century into a major Württemberg stronghold that withstood repeated sieges in the seventeenth century without falling. Napoleon's forces demolished it in 1801 under the terms of the Peace of Lunéville, and what remains, spread over some nine hectares, is described as the largest fortress ruin in Germany. The slopes carry a nature reserve with dry grassland flora and one of Germany's highest vineyards.

What you actually see

• The volcanic plug - a phonolite cone rising from the Hegau plain.
• The ruin extent - about nine hectares of demolished fortifications.
• The Hegau cones - a ring of similar volcanic hills around it.
• The dry grassland - a nature reserve with a vineyard on the slope.

When to go

April to October; the summit is exposed and the walk up takes about half an hour. Open-air concerts are staged in the ruins in summer. Winter access can be icy.

Honest expectations

Everything is ruin, with no roofed buildings. The climb is steady and exposed. Concert evenings restrict normal access.

Nearby

Lake Constance lies east; Switzerland is south.