Last weekend we stayed with 12 guys in Oliver's place. At the agreed time we we're welcomed by a friend of his who gave us 5 spare keys, which was more than enough. It's a very nice place centrally located in the old town and even with 12 guys it was spacious enough.
Because of the nice weather we only slept in the appartment and we're outside for the rest of the time. I'm sure staying in for a day is doable as well.
Anyways... nice place, nice city, nice weather ;-)