The northeast corner of the old city fortification was built from the year 1324. The 26m high, octagonal tower made of quarry stone masonry stands in the middle of a 97m long preserved piece of the old city wall. On the first floor is the former prison of the city of Lahnstein.

A spiral staircase leads up to the second floor with the Schöffensaal. Formerly the guardroom of the tower's crew, it is now used for receptions of the city administration and marriages. The tower also houses the museum of the town of Lahnstein, which documents its rich history with coats of arms, seals and documents.