I spent a weekend last August in Frankfurt, and also drove to the old city of Heidelberg, an interesting sounding place and popular tourist destination which I had been hoping to visit. Heidelberg is an old town, and home to the famous Heidelberg University since 1386. This is the oldest university in Germany, and 5th oldest in central Europe - also rated in the top few universities in Europe, with a focus on research, it has produced 56 Nobel laureates as well as many heads of state and even a Pope. Heidelberg is similar to Cambridge or Oxford in the UK, not so much my university office in Newmarket!
There is an old and mostly-ruined castle overlooking the pretty town and riverside, and the long stone bridge which comes up in almost every photo of Heidelburg! Unlike many historic towns, Heidelburg was spared much damage during WWII, however the castle was already partly destroyed during the Thirty Years' war in 1633, and more again during the Nine Years' war in 1688! Luckily much of the rest of the city is undamaged and unrestored, with old narrow streets and many interesting buildings.
My favourite part of Heidelburg was the 'Studentenkarzer' - the university student's prison! In use from 1780-1914, the prison was used to hold unruly students, particularly those breaching the peace at night. The university held the privilege of disciplining its own students, rather than the local law enforcement, however the student prison was not too arduous, and considered more a right of passage for many students! Of course the students were expected to attend class during the day, and come back to be locked up at night! The students and their fraternity brothers decorated the walls with their names and symbols, which are all preserved until today.