A film by Boas Schwarz Documentary (52min), ZDF/ARTE In summer, bathers flock to the Bay of Pozzuoli. Submerged in the sea just off the beach lie the ruins of an ancient city: Baia. Even the general Gaius Julius Caesar and many Roman emperors after him sought relaxation here. The bay was an exclusive health resort due to its many hot springs. To this day, the thermal activity bears witness to powerful forces bubbling underground: the Phlegraean Fields are a so-called supervolcano that threatens the tourist idyll. Scientists are looking for answers to the question: when will the volcano erupt?