Day 2: The Vatican and Castel Sant'Angelo

Morning: Cross the Tiber to enter the Vatican. Visit St. Peter's Basilica (the largest church in Christendom) and spend time at the Vatican Museums, culminating in the extraordinary Sistine Chapel frescoed by Michelangelo.
Lunch: Stop in the Borgo Pio or Prati neighborhoods for a Roman "pizza al taglio" (crispy and thin) or a porchetta sandwich.
Afternoon: Stroll to Castel Sant'Angelo, Hadrian's ancient mausoleum transformed into a papal fortress. Climb to the terrace for a spectacular view of St. Peter's. End the day by crossing the evocative Ponte Sant'Angelo at sunset.