We stayed in the Constanze room at the ABC Altstadt Apartments and loved it! The room is very clean and bright, with a small kitchenette that has all the necessary equipment and utensils. The apartments are right on Getreidegasse, so the location couldn't be any better. Don't worry about any noise, because the sound proof windows definitely do their job. The hardwood floors slope a bit, which just adds to the charm of this 600 year old house!
Heide was very timely in her responses to emails, and patiently waited in the apartment (even though our train was delayed!) to give us the keys and show us around the room.