google is your friend
https://www.google.nl/maps/search/fkk+club/@49.5799227,7.9094149,8.68z
It seems there is no FKK in Mannheim itself, but there are some closeby. The very big and popular Sharks is not that far away in Darmstadt. In Worms you have Feigenblatt, which is a small club but can be cosy. They claim to be the oldest still active brothel in Germany.https://www.google.nl/maps/search/fkk+club/@49.5799227,7.9094149,8.68z
It seems there is no FKK in Mannheim itself, but there are some closeby. The very big and popular Sharks is not that far away in Darmstadt. In Worms you have Feigenblatt, which is a small club but can be cosy. They claim to be the oldest still active brothel in Germany.
a red light district. Well, to be honest, a long closed off street where they are all on display behind windows.
I was there at least once a week.