This is a unique construction in Bohemia due to its form, and perhaps this is why it has evoked so many questions and legends. The tower is the oldest preserved structure in the castle complex, dating back to around 1230. It has a squared layout, is 20m high, and the walls are 3.5m thick. Its characteristic shape is formed by 44 layers of roughly worked blocks, bulbs, or „hlíza“. The color of the stone sometimes evokes the name „Black Tower“. The beginning of the 20th century still fostered the notion that the tower was a memory from the 2nd century AD, a remnant of Germanic tribes („markoman“).

Today we can see such stone markings not only at Zvíkov, but at other places where the local building company was active (i.e. the royal castle, bridge, and parish church in Písek). Humans, in their creativity, were instead willing to see secret runes.

This room ties together two „realities“ - the Crown Jewels were supposed to be stored here until Karlštejn Castle was built, and the Zvíkov Trickster is active here, haunting the halls at night.