I have to agree with most of the latest reviews - be very careful - what you think you are getting and what you get are 2 entirely different things, especially when you see the photographs of the apartment on the Net. Our apartment was #14 at Gerlgasse 4 , not at Fassengasse 18, as advertised. Maybe there are even more locations, judging by comments by other T A reviewers??? Luckily there was a lift to take us to the 4th floor. The "Apartment" was tiny - open the front door, and straight in front was a double bed bedroom, with a table and chairs for 2 people - yes you eat in the bedroom. The "kitchen" to the right of the front door was 5 feet long and 3 feet wide - definitely a 1 person affair - a two ring electric hot plate, sink and microwave, with a washing machine, but no dishwasher. The bathroom, on the left hand side of the front door was functional and clean but similarly tiny - the hot water system was in the shower, and it was definitely a one person at a time room. Only 1 window in the bedroom, and no ventilation in the kitchen, bathroom or bedroom, so the place was stuffy and it was only 22 degrees Celcius when we were there - it would be a nightmare if there was a heatwave - and there is traffic noise outside. The neighbourhood was very down at heel and the walk into town is a good 30 minutes. There is public transport close by, but no details of how to use it and no ticket machines, in the vicinity, so we had to walk into the Tourist Office in town, get the details of how to use the system and buy our tickets there. From then on we were able to travel easily on the bus, train and tram network.. We parked our car in a Parking Station close by, at a cost of 35Euros per day. Vienna has no all day on-street parking unless you are a resident - all on street parking is for less than 2 hours and the parking inspectors are deadly, so if you are coming by car you either pay the hefty parking fee or "Park and ride" from the outskirts, where parking is around 3Euros per day.You can find more details on the Belvederes website.
The pluses - it was cheap 310 Euros for 4 nights, clean and there were basics such as papertowel, Liquid soap, dishwashing liquid etc provided. The correspondence, by E mail with the managers was helpful and we were met at the apartment and given the key. I would have walked out immediately had I not paid in advance. My advice would be to pay by cash when you get there, rather than the option of paying by CC or PayPal in advance. However you must pay the security/damages deposit before you get there (150Euros), so not sure how that would work with regard to a refund if you were to just walk away.
My recommendation would be to specifically ask where you will be staying and request some photos, otherwise like me you will be really disappointed
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.