Weissenau Castle was first mentioned in the historic record as castrum Wissenowe in 1298. It is unclear whether it was built by the Lords of Rotenfluh (Unspunnen) and then given in fief to the Freiherr of Weissenau or if it was built by the Weissenau family as the center of their estates. The castle was built on what was an island at the mouth of the Aare river into Lake Thun. In the intervening centuries, the waterway silted up and the island became connected to shore. The market town of Widen grew up across the channel from the castle and in 1362 was connected to the castle by a bridge. Around 1334, the Freiherr of Weissenau joined other local nobles in a war against the growing power of the city of Bern. After the defeat of the nobles, Weissenau was forced to sell the castle and Widen to Interlaken Abbey to pay his debts. In 1365, the Abbey moved the weekly markets and yearly fair away from Widen and to the village of Aarmühle (which is now Interlaken). Losing the market devastated Widen and it began to decline.
In 1528, the city of Bern adopted the new faith of the Protestant Reformation and began imposing it on the Bernese Oberland. The Abbey and its villages joined in an unsuccessful rebellion against the new faith. After Bern imposed its will on the Oberland, they secularized the Abbey and annexed all the Abbey lands. Weissenau Castle and the small village of Widen became a part of the Bernese bailiwick of Interlaken. The castle was used as a prison into the 16th century, but began to fall into disrepair and eventually collapsed. In 1655 and again in 1700 the bailiwick made plans to renovate and repair the castle. However, neither plan was implemented.
Today only ruins remain of the castle. The castle residence and tower, portions of the castle building and the curtain wall are all still standing.
References:The Château de Foix dominates the town of Foix. An important tourist site, it is known as a centre of the Cathars. Built on an older 7th-century fortification, the castle is known from 987. In 1002, it was mentioned in the will of Roger I, Count of Carcassonne, who bequeathed the fortress to his youngest child, Bernard. In effect, the family ruling over the region were installed here which allowed them to control access to the upper Ariège valley and to keep surveillance from this strategic point over the lower land, protected behind impregnable walls.
In 1034, the castle became capital of the County of Foix and played a decisive role in medieval military history. During the two following centuries, the castle was home to Counts with shining personalities who became the soul of the Occitan resistance during the crusade against the Albigensians.