Burg Trendelburg, Medieval castle in Trendelburg, Germany.

Burg Trendelburg is a castle on a sandstone spur above the Diemel, at 172 m, with a trapezoidal plan. Its 40 m bergfried, called Rapunzelturm, is built into the west wall and has walls up to 7 m thick and over 130 steps. The main house and three corner towers keep sandstone-slab roofs; a gate tower with a half-timbered top stands at the entrance.

Konrad III of Schöneberg built the castle around 1303 on a sandstone spur above a ford of the Diemel. After he lost his ancestral seat to the Bishopric of Paderborn, the 1306 peace made Trendelburg a joint administrative and judicial seat of Paderborn and Landgrave Henry I of Hesse. In 1465 it passed finally to Hesse, and in 1472 received town rights.

The castle's nickname Rapunzelturm comes from the Brothers Grimm tale, and the German Fairy Tale Route passes through Trendelburg because of it. Local legend also knows five Trendula sagas, including "Trendula lässt Berge entstehen" and "Tod in der Mordkammer", which are separate from the Rapunzel connection.

The castle stands on a sandstone spur above the Diemel, reached from Trendelburg's old town; a rock-cut neck ditch separates it from the houses, crossed by a footbridge. The restored crenellated west wall is walkable, and the bergfried called Rapunzelturm has over 130 steps. The main gate is flanked by two corner towers, one with a timber-framed top.

The bergfried called Rapunzelturm is integrated into the west wall, rises over 40 m, has walls up to 7 m thick and more than 130 steps, plus a dungeon and a separate escape entrance from the courtyard. Four machicolations served its defence, and three original arrow slits survive in the west wall.