We booked an apartment, which is in fact about 5-10 mins walk from the actual hotel, very near the cathedral. The entrance is behind a metal gate leading to the store room of a mini-supermarket. There is no sign saying "Dom Hotel Am Römerbrunnen Apartments" that is visible from the street. There is just a small sign saying Apartments on a wall behind the metal gate but no name on it. It took several minutes to find the way in.
The apartment itself was large, warm and clean, with 4 single beds in a large seating area, a bedroom for one, a dining area a well-equipped kitchen, a toilet and a shower. The shower is in the entrance hall, with just a curtain for privacy - it has no lockable door!
We had breakfast in the hotel on one morning, for which we paid on check-in. At the time we had not been told we would be staying 5-10 minutes away. Two of our party (in their 70s) felt it was too far to walk so I rang reception to request a refund of their breakfasts, but was told this was not possible. The breakfast was not bad - freshly baked croissants, tea, coffee and juice.
On our final morning, we left before 8am to find the metal gate locked from the outside. Our key would not turn the lock from the inside, and an employee of the mini-supermarket told us the lock was broken, so I called reception who sent someone to let us out. In the end, I managed to open the lock by putting my hands through the metal game and accessing the lock from the outside. Not an ideal end to our stay.