Piazza di Spagna with famous Spanish steps
Piazza Navona - well known thanks to Dan Brown book Angels and Demons. You can admire a nice architecture of this square as well as the famous fountains: Fontana dei Quattro Fiumi and Fountain of the Four Rivers with Egyptian obelisk.
Trevi Fountain (Fountain di Trevi) - is the most beautiful and the most largest baroque fountain in Rome. It is a must see attraction.
Colosseum - a top attraction in Rome. Colosseum is the biggest amphitheatre of Roman Empire for gladiatorial games and spectacles.
Capitol
The basilica of San Pietro in Vincoli
The Arch of Constantine - is located near Colosseum and Palatine Hill.
Pantheon - is a temple dedicated to all the gods.
Spanish Steps - the most beautiful sight is from Piazza di Spagna
Santa Maria Maggiore
Catacombs - a maze of underground tunnels
Castel Sant Angelo
Mouth of Truth (Bocca della Verita)
and top attractions in Vatican City
see top rated walking tours: Skip the Line: Vatican City
Sistine Chapel - Michelangelo's famous masterpiece thanks to wall paintings Last Judgement.
Vatican Museums
St. Peter's Basilica (San Pietro)
St. Peter's Square (Piazza San Pietro)