Well, I thought this would be an easy one.....

Anyway, I have found one place in Freiburg who claim to rent out everything including tandems.
Here's the link (all in German, sorry):
https://csbuero-gw49.dyndns.org/mobi...ion/radverleih

however, they had mixed reviews on the racing-bike forum where I found the link. If I find a minute, I can call them and ask what they actually have there.

Cruisers and mountain bikes can be rented in just about every town, the word you are looking for is "radverleih".

Be aware that it is not usual to rent out helmets, so it might be worth taking your own.

I'll let you know if I find anything else.

Bron