In this episode, Alberto Angela proposes a singular journey among the hidden surprises of Rome. "The fourth day" is what tourists always miss. Travel agencies reserve a short time for visiting the city, just three days. In this way many wonders of the capital, suggestive and fascinating like the famous ones, remain hidden. Alberto Angela "reveals" the fourth day, so to speak, hunting for the masterpieces hidden for centuries in the eternal city. Password: what's beyond that facade?