In 1680, 40 fortress inhabitants died of the plague. At the time, infected people were accommodated outside the fortress, as there was no other way to isolate. When the epidemic was over, they preventively extended a natural rock crevice into an isolation room, which was only called “Plague casemate” later. Today, the casemate is eight meters deep. It had an entrance, an air shaft, and a shaft to pass down food. In the late 19th century, it was converted into an artillery observation post. In the process, all the formerly open shafts were closed.