Burg Altenfels, Medieval castle ruins in Brilon, Germany

Burg Altenfels is a castle ruin near Brilon that consisted of two separate fortification structures on a mountain ridge. The eastern remains include sections of outer walls and a northern tower, while the western section no longer exists.

Two forts stood on the 486 m Altenfels. The western one was built in the second half of the 11th century and first named in 1144 in a register of Count Siegfried IV of Boyneburg and Homburg; it appears again in the 1202 partition treaty of Henry the Lion's sons. A bishop's garrison is last recorded in 1326, and archaeology points to destruction in the 14th century. The eastern fort existed from about 1100 until the third quarter of the 12th century, when fire ended it.

The name Altenfels comes from the 486-metre hill on which the castle stands. Visitors can see the excavated eastern castle, where two towers, possibly residential, were protected by ramparts and ditches; no other buildings stood inside. The western castle was destroyed by a quarry in 1968 after a rescue excavation.

The eastern castle remains were excavated, secured and made accessible; the western summit remains were destroyed by a quarry in 1968. The site lies on the 486 m Altenfels, which drops steeply about 150 m to the south. Sturdy footwear helps on the uneven ridge path.

The western section of the castle was completely removed by quarrying operations, while the eastern structure was destroyed by fire in the 12th century. These two different destruction methods shape what visitors see today.