This narrow, approximately 800 meters long corridor connects the City of Vatican with the Castel Sant'Angelo. It was made famous by Dan Brown, as it played a crucial role in his book Angels and Demons (and the movie based on it). It also appeared in the second installment of the famous Assassin's Creed computer game series.
The passage, or passetto in Italian, was built in the 13th century by Pope Nicholas III. Almost two hundred years later, it helped save the life of another Pope, Alexander VI, better known as Rodrigo Borgia, the head of the infamous Borgia family.
If you want to visit the Passage today, you can do so, but only as a part of a visit to the entire Castel Sant'Angelo.
Open only for a limited time each summer and on special occasions.
Wikipedia https://en.wikipedia.org/wiki/Passetto_di_Borgo
Address 23 Borgo Sant'Angelo, Roma 00193, Italy
Coordinates 41°54'11.864" N 12°27'41.49" E