Great stay, and a nice little hotel.
The Graben hotel location is unbeatable. St Stephans cathedral, Hofburg palace, great dining and shopping are all an easy walk, and minutes from the Graben hotel front door.
UBahn (Stephansplatz station) is a 5 minute walk, providing easy access in minutes to the Museums Quartier, Schonbrunn, the Prater. Breakfast was standard, but good quality (cold cuts, cheeses, yogurt, fruit, eggs, sausages, bread and pastries).
All in all a nice little hotel, and I would definitely stay here again.