Château de Frœnsbourg, Medieval rock castle in Lembach, France.

Château de Frœnsbourg sits on an isolated sandstone ridge with two main buildings and rooms carved directly into the rock face. The site stands at about 310 meters elevation and combines above-ground structures with chambers inside the stone.

The castle is attested in 1269 as the property of the lords of Frönsburg; an indirect mention of 1235 is reported by A. Thon. Around the mid-14th century it was divided between the Froensbourg, Loewenstein and Sickingen families. In 1349 it was taken and ruined for the banditry of Reinhard von Sickingen, and in 1358 the Palatine Count became its liege lord. The ruin passed to the Fleckenstein family at the end of the 15th century, was restored around 1481, and was demolished by the French in 1677.

The castle is closed to the public for safety reasons since 11 March 2022, so the rock-cut rooms and staircases cannot currently be visited. The site has been listed as a monument historique since 1898. Its name comes from the Froensbourg family, attested in 1269 and probably a branch of the Fleckensteins, with whom they shared armorial bearings.

The path to the ruins takes about 40 minutes through a forest trail from Frœnsbourg farm between Lembach and Obersteinbach. Sturdy footwear is needed since the path is steep and rocky in places.

The southern rock is reached by a modern footbridge, replacing the original access. The northern keep and southern lodgings on the upper terrace are inaccessible. The castle has been closed to the public since 11 March 2022 for safety reasons.