The Vallone dei Mulini — Valley of the Mills — is a gorge that cuts behind Piazza Tasso, formed some 37,000 years ago by volcanic activity and carved deeper over millennia by two rivers. Medieval stone mills operated here from the 13th century, taking advantage of the water flow. The best view of the valley is from street level: peer over the railing on Via Fuorimura, just behind the main square, and the abandoned mill building drops away below you, its walls entirely covered in ferns and subtropical plants that thrive in the perpetual humidity.
The gorge is not accessible to visitors — it can only be seen from above — but that half-minute looking down into a slice of wild green valley behind one of Italy's busiest tourist squares is one of the most surprising moments in Sorrento. The contrast between the chaos above and the stillness below makes it genuinely memorable.