Where: Part of the main door to a large communal apartment, home to over 20 people, in a prestigious part of the historical center of St. Petersburg.
What: Three doorbells, belonging to different tenants. Usually these are marked with the name of the owner. Perhaps potential visitors know that already. Judging by the ash above the left bell, somebody burned a piece of paper with a name on it.
Often there is also a "common" bell to which all residents respond. Individuals have their own number of rings (Ivanovs, one ring; Petrovs, two rings, and so forth). See the common bell next to the door of this same apartment.