Cologne is great and this is a great area, but pick a different hotel. 0/10
I'm usually very understanding, but wow. AC broken, electrical generally on the fritz, rooms missing some basics like a phone and clock/alarm. When approached about the ac being broken, staff, especially what seemed to be management could only shrug and say "yeah that happens but we can't do anything since we're sold out". This includes when giving a private review after my stay, again, shrug... "we'll look into it and make sure our staff get better training"... Next time, try at least a refund instead of leaving a customer in a roasting-hot room with flickering lights for a week.
To be clear, this isn't some front-desk or general hotel worker's problem, those folks seemed to genuinely care but just had no way to help, if this is known to happen I doubt they had insufficient training given that even when communicating directly they didn't give even a partial refund. I hate to think the lower level might get blamed, but wow worst hotel stay I've had in a long time.