Fort Malakoff Park, Mainz
If you wanna have a rather quiet evening, then this café/bar would be a good option. Even though there are some other bars and a club nearby there really isn't much going on in this corner of the Fort Malakoff Park, which is a kind of roofed shopping centre.
They offer alcoholic and non alcohlic drinks (cocktails, spirits, soft drinks etc.) as well as small dishes.