Weissenau Castle (Ruin) (Unterseen)

The Weissenau ruin was a medieval castle in the municipality of Unterseen in the canton of Bern from the 13th century.

The Weissenau ruin is the largest and best-preserved castle complex in the Bernese Oberland. It is located on a former island at the mouth of the Aare into Lake Thun in today's Neuhaus-Weissenau nature reserve.

The castle and the associated harbor were built in the 13th century as an imperial castle to secure and control the flow of goods over the Alpine passes. In the 13th century, the castle was owned by the Barons of Wädenswil. In 1279, the town of Unterseen was founded, leading to the economic decline of Weissenau Castle. In 1298, it was first mentioned in writing as "castrum de wissenowe". In 1318, Duke Leopold I of Austria pledged the castle to the Lords of Weissenburg. In 1334, they sold the castle to Interlaken Monastery. In 1530, Interlaken Monastery was secularized and the castle passed to the state of Bern. After that, the castle was abandoned and fell into disrepair. Since 1981, the ruin has been a protected monument and was conserved between 1988 and 1989.