The Studentenkarzer was the student prison of Heidelberg University until 1914.
At that time, the university still had its own jurisdiction, so a bailiff could impose carceral punishments. The detention lasted between three days and four weeks, depending on the offense, but the students were allowed to attend their lectures. After university sessions, prisoners had to serve their time in the Karzer. Many passed the time by immortalizing themselves on the walls with their likenesses and sayings. These "works of art" can still be seen today.