The Tower of Fools
Narrenturm is a 2002 novel written by Andrzej Sapkowski. It tells the story of Reinmar of Bielawa, also called Reynevan de Bielau or Reynevan von Bielau. The action takes place in Silesia in 1425, at the time of the Hussite Wars.
The word "Narrenturm" is the German word for "Tower of Fools": a tower in which people suffering from rare and mental diseases were isolated in the Middle Ages.