Considering the Hotel Schottenhof in Mainz?
A VT member wrote the following comment about visiting Mainz:
SWR3 open air festival by Kristina1701
Every July the swr3 open air music festival takes place in the "Regierungsviertel" of Mainz. It usually starts in the early afternoon and ends around midnight. The entry is free so it is always pretty crowded!
The bands performing in the afternoon are usually the not so well-known ones, towards the evening more well-konwn as well as popular bands perfom.
As far as I know you're not allowed to bring your own drinks etc. to the festival but there are lots of drink and food stalls, so no worries ;-)