In 1932, the entrance to a hitherto unknown tunnel was discovered in the ruins of the old Roman resort of Baiae, on the Bay of Naples. Packed with rubble, wreathed in choking gases, and heated to more than 120 degrees Fahrenheit by nearby magma chambers, it was difficult and dangerous to excavate. But when, after 10 long years of work, the amateur team exploring it finally broke through to lower levels, they uncovered something truly remarkable: a complex, pre-dating the Romans, built around a boiling underwater stream that seemed to have been designed to ape a visit to the Greeks’ mythical underworld.
Who built the tunnels at Baiae – and for what purpose? When and why were they blocked up? And do the theories proposed by the discoverers really add up? This week’s Smithsonian essay weighs the evidence.