We knew this ahead of time, but Reception has a hard stop at 11pm and closes the front door. We narrowly made it in ~10:40pm as our train was delayed. Receptionist told us we were late and asked if we knew (about the "deadline", implied); we told them we did and that we'd have emailed to give a headsup if we were going to be later than 11 that night, but I couldn't tell if they accommodate late arrivals and if so, how late. I would not recommend this Hotel to anyone with a chance of arriving past 11pm, or those who plan to stay out past 11pm nightly, to make lives easier on both ends.
Otherwise our stay was pleasant. Room clean, with good facilities. Location adjacent to old town Koblenz -- about 10 minute walk to the Rhine river where KD cruise dock is, Koblenz main train station 16 minute walk or ~7 euro cab ride away . Reception stored our bags for us while we toured Koblenz for a few hours after checkout.