The building, at 12 rue Pétion, dates from the late 1800s. Like many buildings of this period, there is a front part that faces the street, a central courtyard, and a rear part with apartments that face the courtyard. Your apartment is in the rear building, off the street, so there is virtually no street noise.
From the street, you enter a code to push open the large door. In the entry hall, you'll find the post boxes and the stairs for the front building, and another door opening to the central courtyard.

Looking up, you can see your apartment (in the center part of the above image), on the 5th floor (with the shutters opened).
Walk through the courtyard to the rear building to fine the spiral staircase leading up to your apartment. Just to the right of the stairs, you can see the door leading to the caves/basement (access not included) and there is a storage area for bicycles (included).