Michelangelo's last fresco—the crucifixion of St. Peter in the Pauline Chapel.
Royal Hall of the Vatican with Swiss Guard for scale.
Bernini too good
Trevi Fountain goes into the list with the Eiffel Tower, Empire State Building and the Tower of London where they are *ridiculously* over crowded but totally worth it. Maybe the best on that list in terms of effort/payoff ratio.
Caravaggio was good at painting y'all.
Spanish steps (close up)
Formal Roman breakfast attire for al fresco dining