Fodor's Expert Review Rocca Paolina
A labyrinth of little streets, alleys, and arches, this underground city was originally part of a fortress built at the behest of Pope Paul III between 1540 and 1543 to confirm papal dominion over the city. Parts of it were destroyed after the end of papal rule, but much still remains. Begin your visit by taking the escalators that descend through the subterranean ruins from Piazza Italia down to Via Masi. In summer, this is the coolest place in the city.