The small town of Weißensee is proudly overlooked by the eponymous Weißensee Castle - also known as Runneburg. The fortress was built by Landgravine Jutta around 1170 and is now one of the most important examples of Romanesque architecture in Germany. Hardly any other complex has preserved as much original building fabric from the High Middle Ages as here. The castle is considered one of the most important Romanesque secular buildings in Germany. At a strategically important location halfway between Wartburg Castle and Neuenburg Castle near Freyburg, Weißensee became a mainstay of landgrave territorial politics. The complex is surrounded by a ring wall up to 7 m high. The highlights of the medieval architecture are the palace and its five-storey palace tower. The tower contains remarkable examples of medieval stonemasonry, including a branch column with a capital of vines.

In 1998, historian Michael Kirchschlager discovered the Weissensee Purity Law of 1434 for the brewing of beer in the historical archives.

Planned as a hostel, the castle quickly became a fortified complex. Later, the castle-like fortifications were converted into a hunting lodge, a district administration office and an elementary school.