Next to the town hall in the Tourist Info (Merianstr. 2) you can book tickets for a guided tour. There are several guided tours every day. Very entertaining and interesting.
Absolutely recommendable, in every season, whereby I prefer to enjoy the cool on a hot summer day! Tip: Ask for the "photo with the police car" and the "earthquake measuring station" ... Have fun!
stadt-oppenheim.de/oppenheimer-kellerlabyrinth