Weissensee Castle was one of the most modern new buildings of its time. The Landgrave of Thuringia showed off his wealth here. He had the finest building materials used, such as marble columns, but the palas was also the largest room in the area at the time. In addition to the tower-like north-east extension, the palas was given an upper floor in the form of a light-flooded hall covering the entire floor area of the building. The original spatial impression must have been enormous. The architectural aspirations of a princely building can be seen here.

An unusually shaped column was found in the basement. Regularly arranged, stylized branch stumps adorn its shaft and turn it into a tree trunk with an additional grapevine capital – an extremely rare motif of high medieval architectural sculpture in Germany. In addition, a stone oven was built to heat parts of the first floor. A rare testimony to the high aristocratic living comfort of the time. The ingenious system for supplying the castle with warm air is evidence of the innovation of the Thuringians as early as the 12th century. Systematic development of the settlement in front of the castle began around 1200. The clear structure of the town with its visual axis of the castle, town hall and the town church of St. Peter and St. Paul was quite intentional on the part of the medieval town planners.

Excavated finds from the castle well provide vivid evidence of life at Weißensee Castle. In addition to diced dice, fragments of notched wood and toys, there is a very well-preserved leather belt pouch, a hair tiara and a wooden jug turned from a single piece of wood, the shape and material of which can also be found on colored drawings in the Heilberg song manuscript. There is no more vivid way to present the Middle Ages.

Despite numerous later conversions, Weißensee Castle is one of the most important German secular Romanesque buildings.

Incidentally, the name Runneburg is based on the colloquial term “round castle” with reference to the base area. And references to the legendary Battle of Runibergun in 531, when the Franks crushed the Thuringians, have never been found.