Castel Sant’Angelo in Rome Italy

The Mausoleum of Hadrian, usually known as Castel Sant’Angelo (English: Castle of the Holy Angel), is a towering cylindrical building in Parco Adriano, Rome, Italy. It was initially commissioned by the Roman Emperor Hadrian as a mausoleum for himself and his family. The building was later used by the popes as a fortress and castle, and is now a museum. The Castel was once the tallest building in Rome. More info:

Castel Sant'Angelo
Source: Nabil z.a.

castel sant'angelo1
Source: Giuseppe Moscato

Castel Sant' Angelo2
Source: Dionysis K