Tunnel of Eupalinos

An aqueduct tunnel just over a kilometre long, driven through the hill above Pythagoreio in the sixth century BC by Eupalinos of Megara — and dug from both ends simultaneously, meeting in the middle with an error of a few metres, which is why engineers make the pilgrimage. A long section is open to visitors, lit and fitted with a walkway; it is narrow, damp and low in places. Not for anyone who dislikes enclosed spaces, and visitor numbers inside are limited.