Underneath old Naples, there's a mirror of the city – cavernous and deep, this second city has sheltered and nourished Naples for millennia. Napoli Sotterranea dates back to 470 BC when the Greeks created underground cisterns for rainwater, and the Romans expanded on it with an aqueduct that served for centuries.

As you venture lower, you'll be surprised by the 90% humidity. Imagine the intensified heat for the hundreds who sought refuge here as bombs rained down on Naples in the 1940s.