When anyone visits Rome in Italy, especially for the first time, they tend to head to the Colosseum, the Sistine Chapel, Roman Forum and Trevi Fountain. However, there is an old saying, which says, “When in Rome, do as the Romans do.” The following are some off the beaten track and, let’s face it, rather weird sights to see on a Rome vacation and locals probably know of a lot more.

1. Mamertine Prison

Our first stop on a weird tour of Rome was previously a Roman prison. Located on the slopes of the Capitoline Hill, the Mamertine Prison is hidden beneath the San Guiseppe dei Falegnami church.

Built somewhere around 640 to 616 BC, changes were made in the church by a former king of Rome, Ancus Marcius. The basement room was originally built as a cistern to store water, but the Romans got the idea to re-purpose it, making it into a gloomy dungeon.

Its former inmates were lowered through an opening in its ceiling and likely spent a dreary time down there. They were in good company, however, as according to legend, both Saint Peter and Saint Paul were imprisoned in the dungeon at some time. In fact there is an altar inside the dungeon, with a cross hung upside down, which while normally would be a satanic emblem.

However, in this case it is dedicated to Saint Peter, who the Romans apparently crucified upside down. There are also two busts of the saints standing on the altar.

Take a brief tour of this scary dungeon in the video included below.

2. The 'Mouth of Truth’ – an ancient lie detector

Our next stop on our tour is what could be considered to be an ancient lie detector.

Known in Italian as the “Bocca della Verità,” the “Mouth Of Truth" is a carving, located in the entrance to the Santa Maria in Cosmedin Church. It is believed to have originally been part of a 1st-century Roman fountain, carved with the face of a Roman god. According to a View on Cities, others think it may have been an ancient version of a manhole cover, portraying a pagan god.

Whatever its true background, these days the “Mouth of Truth” is believed to work like a lie detector. Legend says if you put your hand into the mouth of the carving and tell a lie, your hand will be bitten off. Rather amusingly, this fascinating artifact appeared in the 1953 film “Roman Holiday,” starring Gregory Peck and Audrey Hepburn. In the romantic film, Peck plays a prank on Hepburn, which is included in a video clip below.

3. Peeking through a keyhole at Santa Maria del Priorato

Most people believe it isn’t polite to peek through keyholes.

However, on the Aventine Hill in Rome, there is a nondescript door which gives voyeurs a perfect, beautifully framed vision of the dome of St. Peter’s Basilica.

As reported by Atlas Obscura, the most recent occupiers of the building were the Knights of Malta, but there have been many legendary occupants in this fascinating building in the past. The building started out life as a fortified palace for King Alberico II between the years 932 and 954. It later became a Benedictine monastery before being taken over by the Knights Templar in around 1100 and eventually handed down to the Knights of Malta.

These days the historic building is a church, dubbed Santa Maria del Priorato, but throughout those hundreds of years, the keyhole has continued reveal the garden of the building, thus giving a perfect view of St.

Peters and the Vatican in the background. No one knows if this incredible view was planned or just a coincidence, but nowadays tourists can enjoy peeking through the keyhole, instead of just knights.

There are more intriguing attractions waiting to be uncovered while on vacation in Italy. The best advice is, when in Rome, ask a friendly Roman to show you the way.