"You're fine. Just don't look down." I hold my breath, take the captain's outstretched hand and board the boat. The waves glimmer beneath my feet; the only thing separating me from the sea is a pane of glass. As our tour sets sail, the vast Bay of Cartaromana opens up before us.

Jagged cliffs shoot up from the waves; sunbathers sprawl on the inlet bridge leading to the 2,500-year-old Aragonese Castle, attached to the island like the tail of a whale periscoping through the waves. After just 10 minutes at sea, we reach a network of buoys marking the ruins below. I press my hands against the vessel's transparent bottom.