Home to pretty treasures, Velletri is Italy's best kept secret. The nearest major city to Velletri is Rome. Attractions in Rome include Colosseum, St Peters Basilica, Pantheon. Also, to reach Velletri, you'll have to take a flight to Rome; so its not really a detour. And even if it is, the city is worth paying at least a quick visit. Most online packages to this city are of 1-2 days.
Yes,it is that simple really! Enjoy your trip! Keep travelling!