Werdenfels Castle, Medieval castle ruins near Garmisch-Partenkirchen, Germany.

Werdenfels Castle is a ruined fortress perched on a rocky outcrop high above the Loisach valley, between Garmisch-Partenkirchen and Farchant in Bavaria. Stone walls still outline the remains of residential buildings, enclosure walls, and underground chambers that give a sense of how the site was once arranged.

The builder and original purpose of Werdenfels are unknown; construction is dated between 1180 and 1230. From 1249 the fortress belonged to the Prince-Bishopric of Freising, and after the County of Werdenfels was formed it served as administrative and judicial seat. In 1632 the governor's seat moved to a new Amtshaus on the Wang, and from 1676 the ruin was quarried for stone.

The name Werdenfels comes from the County of Werdenfels, the Freising territory whose administrative seat the castle was until 1632; the district name preserves it. The county was called "the best part of the Imperial Principality of Freising" and supplied chamois and red deer venison, wood and marble, floated down the Isar and Loisach to Freising. An 1806 Munich official complained that "many Werdenfelßer still have no Bavarian heart!"

The ruins stand at 795 m on an eastern spur of the Kramerspitz, about 80 m above the Loisach valley floor, and are reached on well-signposted paths; the final stretch is steep and rocky, so wear sturdy shoes. The site is freely accessible at all times and there is no refreshment point, so bring water. The terrain falls steeply from northeast to southeast into the valley, while the ground southwest of the walls rises quickly.

The bergfried, the castle's only truly defensible structure, stood at the northwest corner of the inner ward but was demolished around 1728/30, leaving a rubble mound. In the 15th and 16th centuries it also served as a gaol. Castle researcher Otto Piper noted that the surviving walls conspicuously lack any provision for sustained defence.