The above structure is the Temple of Antoninus and Faustina, originally built in the year 141. It is currently in the Roman Forum area in the center of of Rome, and contains a number of ancient structures dating back to Rome’s heyday as an empire. Along with the Colosseum and Vatican, the Forum will certainly be on the itinerary of whatever tours to Italy you might take.
The Temple of Antoninus and Faustina was built by Emperor Antoninus Pius and was initially dedicated to his deceased wife, Faustina the Elder. When Antoninus Pius died in 161, the temple was re-dedicated to Antoninus and Faustina at the behest of his successor, Marcus Aurelius. It was later converted to a Roman Catholic church, known as San Lorenzo in Miranda, sometime in the 7th century.
I visited the Forum while on a trip to Rome and Venice in 2005. While I would love to go back someday, I would prefer one of the Italy tours that focuses on the countryside, perhaps in Tuscany.