This episode of Ulysses will set off on a journey in search of disappeared cities, capitals of ancient civilizations which after a grandiose development were abandoned and forgotten for centuries. We will see how history, but also nature, have continuously erased and rebuilt places that seemed eternal. And will the cities in which we live today still exist, as they are, in a thousand, ten thousand years? We will see how a city can disappear, suddenly, in the space of a few hours, when the forces of nature are unleashed. Alberto Angela in Santorini will tell how one of the most flourishing centers of antiquity was destroyed by a volcanic eruption. During the episode we will also discover hidden cities, secret cities, invisible cities, cities under cities. We will visit secret US Cold War bases and London's complex underground shelter system.