I had the worst stay of my life at this hotel. It is unbearable during very warm days, as the lay afternoon sun hits its walls, which lack any isolation beyond its masonry. I could not tolerate the heat emanating from the walls and floor, and when I tried to open the windows, the noise of the tram stop right below my 2nd story room was impossible to ignore. There was a rather powerful fan available, but it useless in a room at such high temperatures. The staff tried to help, but the alternative rooms were even warmer.
For the second night, they moved me to a room facing the back. While it was much cooler, it also suffered from the noise of large cargo trucks servicing a supermarket at the back street late at night.
In any case, avoid this when Bonn is warm.