During an eclipse dozens of catostrophes erupted around the globe like tsunamis that could topple down the biggest cities, heat waves that would melt metal in the span of an hour and earth shattering earthquakes that opened up immense Chasms in the ground. Turned out that dozens of kilometers underground humans found massive ancient cities in an open space being the size of a continent. After entering the city, all the exits and holes were either buried or collapsed themself letting out massive amounts of radiation, lava and other dangerous substances meaning they could not leave ever again.
