Burg Arnstein, Rock castle ruin in the Kirnitzsch Valley, Saxony, Germany

Burg Arnstein is a rock castle in the Kirnitzsch Valley near Sebnitz, Germany, built directly into a sandstone cliff. The remains include carved stone steps, slots for wooden supports, underground chambers, a water cistern, and a dungeon, all cut into the rock itself.

The castle was first mentioned in writing in 1436, when it was held by Sigmund von Wartenberg. Shortly after, the Electorate of Saxony and the Six Towns Alliance laid siege to it, and the fortress gradually fell out of use.

The name Arnstein refers to the rock formation on which the site stands, and it is closely tied to local legend. Visitors who reach the top can see steps and chambers cut into the sandstone, showing how the rock was once used as both shelter and stronghold.

The site is reached on foot along a hiking trail that begins at Buschmühle and passes through the Kirnitzsch Valley. The path is steep and rocky, so sturdy footwear and enough time to walk at a comfortable pace are strongly advised.

The rock carvings at Arnstein are prehistoric, not later visitor graffiti. The site also includes the Arnsteinhöhle cave, listed as no. 5051/SH-03 in the Saxon cave register, which was incorporated into the castle's defences. In 1987/88, excavations in the cistern, prompted by a legend about a hidden treasure, found nothing.