The so-called "comfort double room" we booked (picture: huge windows overlooking the Danube, big room with bath, bright and nice) turned out to be a dark, tiny loft with a narrow slit of a window where you can only see the sky unless you're standing in the windowsill. Not even the bathtub was real. Took half an hour arguing with an extremely rude receptionist ("We are fully booked! I can't do anything! Tell me, what should I do?" <- not our job to tell you how to fix it, we just wanted you to help us) and retreating dejectedly to our room before we were finally informed that we would get "the correct room" the next day.
We did get "the correct room" the next day, and that was very nice, just as advertised - would have been a positive review if we got it right away.
Insult to injury: When we asked what to do about the fact that we had to spend one night in the wrong room, we were told we would have to talk to the manager during checkout, because they were currently on Easter holiday, but would be back on Monday. Guess who was, in fact, still on holiday on Monday (hint: the manager). As such, our problem has still not been resolved and is pending a slow email process. Very cool.