Burg Freienstein, Medieval castle ruins in Gammelsbach, Germany.

Burg Freienstein is a castle ruin on Weckberg mountain near Gammelsbach, consisting of stone walls and foundations scattered across the hilltop. Its elevated location offers wide views over the surrounding landscape and reveals the typical layout of a medieval defensive stronghold.

Burg Freienstein was first mentioned in 1297, likely built amid the break-up of Lorsch Abbey's lands between the Palatinate, the Schenken of Erbach and Mainz. From 1398 the Palatinate enfeoffed the Erbach family with the whole castle, which stayed in their hands and served as the seat of the Amt Freienstein. Around 1550 it was rebuilt as a residential castle; from the Thirty Years' War it decayed, was plundered by Bavarian cavalry in May 1622, and after Beerfelden's 1810 fire its stone was taken for rebuilding.

The castle gave its name to the Amt Freienstein, the administrative district it once governed. From 1280 the Lords of Freienstein are documented, later serving as Erbach castle men. The Erbach counts kept the castle as a secondary residence and hunting lodge, and it remained in their possession until the line died out in 1503.

The site is accessible via marked hiking trails from the village of Gammelsbach and sits on a hillside. Wear sturdy shoes as the climb is steep and the ground can be uneven in places.

The castle's shield wall, built to protect the core against fire from the higher mountain, still stands up to 24 m high and 2.50 m thick. In 1938 it was lowered by three metres; a tie rod installed around 1890 remains visible.