Túnnel of Eupalinos

You'll walk through one of the world's oldest engineering marvels - a 1,036-meter ancient aqueduct tunnel carved straight through Mount Kastro over 2,500 years ago. The accessible 200-meter section lets you experience the ingenious clay pipe system that once supplied water to ancient Samos, with plenty of spots where you'll need to duck and weave through the narrow passages. This UNESCO World Heritage site is remarkable for being only the second known tunnel in history to be dug from both ends simultaneously, meeting perfectly in the middle.