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 du Haut-Koenigsbourg is situated in a strategic area on a rocky spur overlooking the Upper Rhine Plain, it was used by successive powers from the Middle Ages until the Thirty Years' War when it was abandoned. From 1900 to 1908 it was rebuilt at the behest of the German kaiser Wilhelm II. Today it is a major tourist site, attracting more than 500,000 visitors a year.
The first records of a castle built by the Hohenstaufens date back to 1147. The fortress changed its name to Koenigsburg (royal castle) around 1157. The castle was handed over to the Tiersteins by the Habsburgs following its destruction in 1462. They rebuilt and enlarged it, installing a defensive system designed to withstand artillery fire.
The fortification work accomplished over the 15th century did not suffice to keep the Swedish artillery at bay during the Thirty Years War, and the defences were overrun.