What stands out to me about the Contel Mainz was how spacious the standard rooms were. Very unusual for a European Hotel and almost like a condominium with a full kitchenette and a connecting hallway between the bathroom and the living/sleeping quarters.
Other plusses included a very nice Italian Restaurant (although i was in the mood for German fare being in Germany...) connected to the hotel, very good service and clean. I am a smoker so this is important to me in terms of such rooms being available and I was accomodated in the Smokers wing of the facility.
Only drawbacks were that it was away from the downtown quite a bit and up a steep hill to get to on foot but at least I got my exercise each day.
