Considered the first great building of the High Renaissance, Bramante’s sublime tempietto (Little Temple; 1508) is a perfect surprise, squeezed into the courtyard of the Chiesa di San Pietro in Montorio, on the spot where St Peter is said to have been crucified. It's small but perfectly formed; its classically inspired design and ideal proportions epitomise the Renaissance zeitgeist.
It has a circular interior surrounded by 16 columns and topped by a classical frieze, elegant balustrade and dome. More than a century later, in 1628, Bernini added a staircase. Bernini also contributed a chapel to the adjacent church, the last resting place of Beatrice Cenci, an Italian noblewoman who helped murder her abusive father in the 16th century, and subsequently was tried and beheaded on Ponte Sant'Angelo.
It’s quite a climb up to the church, but it's an ideal stop on a walking tour of Gianicolo. Take bus 115 from the Viale di Trastevere. The tempietto is reached through the Spanish Royal Academy entrance to the north of the church. If you can get access to the academy's upper level, there are magnificent views of Rome.