A trip to Italy means inevitably delving into the country's remarkable past even if you're not a history buff. Everywhere you go, ornate architecture, art, and even natural topography from various historical periods form a constant canvas of interesting sights. Sometimes, to see how deep Italy's history (literally) goes, you must go underground.

Naples, one of the country's many iconic destinations, features hundreds of kilometers of underground passages that were originally built by the Greeks over 2,000 years ago. Since then, they've been molded and repurposed according to the needs of various empires, and now form an intriguing cross-section of the region's varied history. A tour through the Naples Underground or Napoli Sotterranea takes you far below the city, through ancient theatres, aqueducts, and even air raid shelters.