This is the stairs to the private rooms of the Pope. The top door is the enterance to the Pope's quarters. To its left is where the back entrance to the Sistine chapel is present.
Patio of St Gregory the Illuminator
The northernmost door is the "Holy Door" which, by tradition, is walled-up with bricks, and opened only for holy years such as the Jubilee year by the Pope. The present door is bronze and was designed by Vico Consorti in 1950