Burgruine Steinenschloss, Medieval castle ruins in Thaleischweiler-Fröschen, Germany.

Burgruine Steinenschloss is a ruined hill castle on a sandstone rock above the confluence of the Schwarzbach and Rodalb. Its 70-metre-long, 46-metre-wide ring wall of dressed sandstone blocks, some with bossed faces, encloses an upper and lower ward; a rock-cut passage leads to the upper ward, where a round tower with 2.50-metre-thick walls and an outer diameter of 13.5 metres has been rebuilt to a height of 10 metres.

Built around 1100, probably by the Counts of Leiningen, the castle was destroyed by fire a few years after its massive round tower was added between 1125 and 1166. A 1237 charter already records it as ruined, and it was never rebuilt. In the 19th century the ruin was quarried away, its stones used for houses and for the 1875 Pirmasens Nord station.

The name Steinenschloss comes from the abandoned settlement of Steinen, Steigen or Stegen below the hill, first recorded as "Steiner-Schloss" in 1564. The alternative name Atzenstein, after a nearby farm, is rejected by name researchers. Since 1973 the Burgverein Steinenschloss and later the local heritage society have cared for the excavations.

The site is accessible year-round with trails suitable for walking, though conditions are best during drier months. Sturdy footwear is advisable since the ruins sit on sloped terrain with uneven ground.

The round tower's interior diameter is 8.50 metres, and its walls are 2.50 metres thick, giving an exterior diameter of 13.5 metres. Built between about 1125 and 1166, after the castle itself, it is one of the largest towers of its period in Rhineland-Palatinate. Since 1989/90 it has been rebuilt to a height of 10 metres using stone blocks up to 1 metre long and 55 cm high.