Sain Shermin is a small bed & breakfast hotel located on the second floor of an apartment building in downtown of Vienna, near Vienna Technical University and a few blocks from opera house. The door of the building and the hotel are always locked, and you need to have a numerical code to enter. The staff is always there from 7:00 to 13:00, and sometimes they stay later hours. The staff is friendly. There are plenty of restaurants, sightseeing and shopping around.
However, I did not like the hotel as soon as I entered it. It smells terrible and I immediately got allergy symptoms. The air in the corridor and in my room (#12) had a bad smell. I have no idea what created the smell, but it is likely mold. I notified the staff and asked if they have air purifier. They did not have. They recommended me to open window and turn on a fan in bathroom. I then called Expedia (the room was booked through Expedia), explained the situation and asked if I can cancel the reservation and move to other hotel. (There are plenty of hotels around.) The Expedia representative contacted the owner of the hotel and the owner said that I can leave but they will not reimburse my expenses (7 night stay, 1-8 July, $150 a night). I could not afford these losses. Opened window and fan helped a little and I survived Saturday and Sunday. On Monday, the staff did cleaning, vented the corridors, sprayed with air fresheners, and the "mold" smell was shielded. I do not recommend this hotel.