Altdahn Castle, Rock castle in Dahn, Germany.

Altdahn is a castle ruin on two reddish sandstone outcrops in the Palatinate Forest, its remains stretching about 100 metres. The lower ward has a horseshoe-shaped gun turret to the north and a similar tower to the south; the upper ward keeps the north wall of the palas and a garderobe watchtower. A round, downward-tapering hollow in the rock, exposed by the 1820 rockfall, is read as a cistern or dungeon.

The castle was built in the early 1200s and suffered multiple destructions, including conflicts with neighboring lords in 1363 and attacks by French troops in 1689. These repeated assaults shaped the site over the centuries.

The castle's name distinguishes it from the two neighbouring ruins on the same ridge, Grafendahn and Tanstein. In the museum, shown by telephone appointment, are copies of watercolours that Felix Mendelssohn Bartholdy painted of the ruin on 5 August 1844, and a medieval silver spoon bearing the coat of arms of the lords of Dahn.

Access is through the northeast entrance, where sections of the original gateway and a water-filled defensive ditch are still visible. Wear sturdy shoes, as the terrain is uneven and paths wind across rocky ground.

The site is part of a group of three nearby castles that together with Grafendahn and Tanstein formed a defensive line along a single rocky ridge. This close arrangement reveals how rulers of the time strategically positioned their fortifications to protect a region.