The Borgo is the wedge of Rome between Castel Sant'Angelo and St Peter's, and it carries the city's longest sightline and one of its sharpest arguments. The argument is Via della Conciliazione: the avenue Mussolini bulldozed through a dense medieval quarter in the 1930s to open a ceremonial approach to the basilica. What it gained in grandeur it paid for in lanes.
Begin at Castel Sant'Angelo, Hadrian's mausoleum turned fortress, and cross the Ponte Sant'Angelo past Bernini's angels for the framed view back. Then duck into Borgo Pio, the one old lane that survived the demolition — cobbles, trattorie, washing on the line. Above it runs the Passetto, the walled corridor popes fled along when the city was sacked.
Out onto the Conciliazione, walk its centre and let the dome rise toward you. The avenue delivers you to Piazza San Pietro and Bernini's colonnade. Find the paving disc, stand on it, watch four rows of columns collapse into one — then the obelisk, dragged here in 1586 in total ordered silence. Back to Ottaviano when you're done.