Burg Altweilnau, Medieval castle in Altweilnau, Germany

Burg Altweilnau is the ruin of a hilltop castle on a rocky spur above the Weiltal at 360 m, with a triangular layout. Its main feature is the round bergfried, 8.7 m across and 17.6 m high, whose high entrance at 7.2 m is reached by an external metal spiral staircase. Parts of the ring wall and a square gate tower with a hipped roof also survive.

The castle was built around 1200 by the Counts of Diez and first mentioned as Wilnawe in 1208; dendrochronology of wood inside the bergfried confirms it already stood then. In 1336 Altweilnau held town rights for nine days, and walls and a gate tower were built. The castle was inhabited until 1563, abandoned from 1608, and decayed during the Thirty Years' War; its stones were later reused in Altweilnau houses.

The square gate tower from the 14th century once signaled time and news to surrounding villages. Today it remains the defining feature of the fortress and shows how closely the castle was tied to life in the region.

The tower's viewing platform at 16.6 m is reached by an external metal spiral staircase, then a narrow stone stair inside the wall and a cast-iron spiral stair. The inner diameter at the high entrance is 2.7 m. The site is a ruin on a rocky spur, so expect uneven ground.

The round tower is accessed by an external metal staircase attached to its outer wall, giving the structure an unusual technical character. These later modifications show how the fortress was adapted over the centuries to remain in use.