The Evil Apartment
Bolshaya Sadovaya, No 10. Bulgakov lived here in apartments 50 and 34 from 1921 to 1924.
Here's a view of the facade of the building in the 1920s:
Bulgakov's apartment, and presumably the prototype of the evil apartment No. 50 was through the archway into the courtyard and up a stair to the left. Here's what the courtyard looks like today: