Scharfenburg, Medieval fortified tower in Ruhla, Germany.

Scharfenburg is a ruined hilltop castle on the conical Scharfenberg above Thal. Its round bergfried, about 12 m in diameter with walls over 2 m thick at the base, was rebuilt to 20 m and is reached by an external steel spiral staircase. Below it, remains of ring walls, a wall-and-ditch system and a gatehouse with a Gothic portal and the Uetterodt coat of arms survive.

Scharfenburg was first documented on 13 September 1137, when Hartung von Scharfenberg appears as a witness in a charter for the hospital at Frauenbreitungen. In 1260 Hessian troops occupied it, followed by Wettin ministeriales. From 1446, after a siege in the Saxon Fratricidal War, it lay largely in ruins, and the von Uetterodt family built an administrative house in the valley instead.

The keep holds a small museum with selected finds and information panels on the castle's history, and a small stage in the centre of the courtyard is used for music and lectures. A castle festival is held every July within the walls, and a small log cabin built in 1997 serves the running of the ruin.

The main access is a narrow path starting at Am Rögis on the Scharfenberg, about 75 m above the valley floor. The keep is opened during the day by an automatic locking system; between May and September it is accessible from 9 am to 8 pm, from October to April from 10 am to 4 pm. An external steel spiral staircase leads up to the viewing platform.

The coat of arms of the von Uetterodt family still adorns the entrance gate, a reminder of their long rule from the 15th century until the 19th century. This visible marking shows how noble families displayed their power through such symbols.