1st things 1st: To unlock the building's main door, push the key fully in, then pull it out slightly, and it will turn without effort (pulling or pushing the door is unnecessary and does not help).
Overall we loved our 10 day stay in the apartment. The building oozes history, the interior is nicely decorated (the beds being the only exception, since they alas have some cheap looking plastic end pieces - you can see it in one of the photos), the bedrooms and the living room are spacious, and the view of the Grand Canal and its hustle and bustle is simply fantastic. Some things you might consider before booking: Anyone with a height of around 1.75 m (5.75 ft) will have to duck for about one meter when moving through the narrow hallway that connects the bedrooms with the living area. The wifi only covers the living room, in the bathrooms the signal is already extremely weak (same goes for mobile data connection). The kitchen and the bathrooms are quite narrow (the windowless shower on the other hand felt spacious even for a stronger built 6 ft guy). The apartment gets humid quickly, if ac is not running; since there is no ac in the bathrooms, it is hard to get humidity out of them. While the (blocky) mobile ac unit in the living room had no problems handling the room, the round unit in the master bedroom struggled to cool down the room. There is also no seperate ac unit for the 2nd bedroom, and the only way to install one would mean you would have to leave the door into the building's courtyard open, which we would advise against, since we encountered both the front gate and the building's main door not having been properly closed at one point during our stay. The living room, even with all lights on, is relatively dark once the sun sets (but one can still e.g. work on a laptop).