It is a large, old and classical apartment building which is run by the estate company. You enter with a password and key box, so it is really easy to check in. The building itself is very nice with fancy walls and ceiling etc. It is really a place you want to stay when you want to visit Vienna as it really has a soul. The apartment itself is also the same, it is furnished really fine, we loved the paintings particularly. But of course it is a really old building, so classical wooden pavement makes sound when you walk on it (the same pavement with the museums and palaces etc.). But this gives even more character on the apartment.
The only things i would slightly complain would be: internet was slow in the first two days, but than it get better. TV has no internet connection but local channels work, and there is no cattle to heat up water for tea etc, (only coffee machine). but those didn't bother us well, it was a fantastic stay.
An important note: apartment has no parking place! it is really hard to find parkings and expensive in Vienna, so check and plan carefully if you will rent a car etc.
Overall, we are glad that we stayed here, this apartment really adds up value on a Vienna city trip.