Alt Wädenswil Castle, Castle ruin in Richterswil, Switzerland

Alt Wädenswil Castle is a hilltop ruin above Burghalden station in Richterswil. Its oldest element, the Freiherrenturm, was built before 1200 with outer walls of large glacial boulders. In the 14th century the Johanniter added a moat and a thirteen-room convent building with dormitory, refectory, pilgrim hostel and chapel; a turreted outer wall followed in the 15th century.

The castle was first documented in 1265, though the Freiherren von Wädenswil, mentioned in a 1130 charter of Fahr Abbey, built their seat in the 13th century. The pre-1200 Freiherrenturm, with outer walls of large glacial boulders, is the oldest part. In 1287 Rudolf III sold the lordship to the Johanniter house of Bubikon, which in the 14th century built an order castle with a new moat and thirteen rooms.

The name Wädenswil comes from the Freiherren von Wädenswil, first recorded as Wadinswilere in 1130. After 1549 the site belonged to the Zurich Landvogtei, and the castle was deliberately slighted in 1557. The ruin later served as a quarry, and in the 1870s parts were blown up for railway construction.

The ruins are accessible at any time as they sit freely exposed on a hillside that can be reached on foot. There are no admission fees, but visitors should be prepared for uneven ground and sloped terrain throughout the site.

In the 1870s parts of the ruin were blown up to supply stone for the Wädenswil–Einsiedeln railway line. The site had already served as a quarry for centuries before that. A committee bought the castle grounds in 1900, and a foundation for its preservation was created in 1902.