Burg Altwinnenden, Medieval castle ruins in Winnenden, Germany.

Burg Altwinnenden is a castle ruin perched on a hilltop near Winnenden with a stone keep dating to the 12th century as its main feature. The site consists of several levels with the well-preserved keep standing as the most visible element of the former fortification.

The Lords of Winnenden built the castle in the first half of the 12th century, and Gottfried von Winnenden erected the keep on the spur in 1181. It was first mentioned as "castrum Winidum" in 1210 and enlarged in 1212 and 1225. Through Luitgard von Neuffen's marriage to Konrad von Weinsberg, it passed to the Weinsbergs, who sold it to Count Ulrich III of Württemberg in 1325 for 4600 Heller. It fell into ruin in the 15th century and was demolished between 1536 and 1538 except for the keep; Duke Ulrich had the stones taken to Schorndorf for the castle and town wall. In 1581 the community of Bürg bought the ruins and land for 310 Gulden.

The name Altwinnenden distinguishes the ruin from the later town castle, while locals also call it Burg Bürg after the village of Bürg. The tower now belongs to a hotel built around it, so the former castle site is used for hospitality rather than defence.

The keep stands on a hill spur above the Höfen-Stöckenhof road in the Bürg district, but it is enclosed on two sides by a hotel and is not open to the public. Visitors can only view the 23-metre tower from outside. The hotel buildings around it have been repeatedly extended.

The castle keep was built so solidly that it withstood demolition while everything else was torn down. This sturdy construction makes the tower the only visible reminder of what once was a substantial fortress.