In a word: extraordinary. In 524 BC, when Pythagorio (then called Samos) was the island’s capital and a bustling metropolis of 80,000, securing sources for drinking water became crucial. To solve the problem, ruler Polycrates ordered labourers to dig into a mountainside according to the exacting plan of his ingenious engineer, Evpalinos. Many workers died during the dangerous dig, but the result was the 1034m-long Evpalinos Tunnel. In medieval times, locals used it to hide from pirates.