Bolsena Caldera (Italy)
Beneath idyllic Lake Bolsena lies a supervolcano that hasn’t erupted for 370,000 years. Medieval towns dot shorelines where subtle seismic activity and gas bubbles hint at the restless magma below. Farmers tend vineyards on fertile volcanic soil. Tourists swim and sail, unaware of what created the picturesque lake. Scientists note that even long-dormant calderas can reawaken with devastating consequences.