Zähringen castle, Medieval castle ruins in Gundelfingen, Germany.

Zähringen Castle is a ruined hilltop fortification on a spur of the Roßkopf at 478.3 m above sea level near Gundelfingen. Its surviving 18-metre round tower, built in the 13th century, has a crenellated top with merlons and an observation platform. The rough tan, beige and grey masonry includes a large rectangular opening with a pale lintel, a small red-brick recess, and a round-arched doorway near the base, with ivy climbing the lower left side.

The castle was originally the family seat of the Zähringers but was abandoned in 1091 when the ruling family moved their power center to Freiburg. After the family line died out in the early 1200s, the stronghold came under imperial control.

The castle gave its name to the Zähringer dynasty, whose members founded Freiburg im Breisgau, Bern, Villingen, Thun, Rheinfelden and Murten. Since 1851 the Freiburg student fraternity Teutonia has held its foundation festival at the ruins. The round tower serves as an observation deck.

The castle hill is reached by car only from Freiburg-Zähringen via the Pochgasse; from Gundelfingen-Wildtal, marked hiking trails lead up to the ruins. A restaurant on the hill offers diners a view of the valley. The 18-metre round tower has an observation deck surrounded by merlons.

The 1128 Rotulus Sanpetrinus, a parchment roll from the nearby Abbey of St. Peter, records the castle as "apud castrum Zaringen". The document was issued at the castle itself, which makes it the first unambiguous written proof of the site.