Burg Wendelstein, Medieval castle in Vacha, Germany.

Burg Wendelstein is a medieval castle in Vacha with a rectangular layout of approximately 60 by 80 meters and massive outer walls. The structure sits near the Werra River bank and functions today as a museum.

Burg Wendelstein was founded under Abbot Heinrich IV of Fulda and first mentioned in 1294. It was incorporated into Vacha's town fortifications as the northeastern stronghold, and from 1406 it was permanently pledged to Landgrave Hermann II of Hesse, becoming a Hessian administrative seat. It survived the great town fire of 1467.

The museum's puppet collection of around 2,000 pieces comes from the private collection of Vacha resident Elenor Fischer. A memorial plaque on the castle wall commemorates Hans Sippel, leader of the Werrahaufen of rebellious peasants, captured and executed in Eisenach in 1525.

The castle stands on the northern edge of Vacha's old town, about 100 metres from the Werra. The town-side walls were demolished in the 19th century, so the grounds are approached from the town centre; the round tower in the southwest corner is about 20 metres high and its entrance lies some 10 metres up.

The round tower in the southwest corner stands about 20 metres high with walls 2 metres thick; its only entrance was a small door about 10 metres up, reached by ladder. The castle is also known as Winterstein, and a plaque on its wall commemorates Hans Sippel, leader of the rebellious Werrahaufen peasants, captured in 1525 and executed in Eisenach.