The Town Fortification can be visited
Town Fortification Andernach-Round Tower

The northwestern corner of the medieval city fortifications of Andernach is shaped by the Round Tower, a defensive tower from the 15th century. It is considered one of the most powerful of its kind from that era.
History+
The construction of the Round Tower took place in two main phases. The round substructure was started before 1440, possibly even between 1412 and 1415, as building accounts suggest. Between 1448 and 1453, the octagonal superstructure was added. The construction manager for this second phase was the municipal master builder Philipp Preudemann. The tower served as a watch and defensive tower and was a symbol of civic consciousness against the Archbishop of Cologne. In 1689, the tower withstood an attempt by French troops to blow it up. In the 19th century, it narrowly escaped a planned demolition and was renovated in 1880.
Image: http://commons.wikimedia.org/wiki/File:Andernach_-_Konrad-Adenauer-Allee-K%C3%B6lner_Stra%C3%9Fe_-_Runder_Turm_01_ies.jpg?uselang=de
Location: 50.4408, 7.3964