Janiculum Hill is the second-tallest hill in Rome and arguably the most beautiful one as well. It also offers some of the best views of the city of Rome, making it quite popular among visitors. Last but not the least, Janiculum hides several interesting sights of its own, be it a baroque fountain from the 17th century, or a shrine designed by Bramante.
Since it lies west of Tiber and outside the location of ancient Rome, Janiculum is not counted among the famous Seven Hills of Rome. However, it is actually part of the historical legacy of Rome just as much as them, since it used to be the place of worship for an ancient god Janus, all the way back to the Roman days.
The square at the top of Janiculum is usually not too crowded with tourists, however, the hill is a bit removed from the center of Rome and it takes a while to reach its top. If you do not fancy lengthy walks, consider taking a taxi to drive you up.
Wikipedia https://en.wikipedia.org/wiki/Janiculum
Address Via Garibaldi and Passeggiata del Gianicolo, Rome, Latium, 00149, Italy
Coordinates 41°53'30.352" N 12°27'38.927" E