Ulisse will dedicate his third appointment to the underground world, making a journey beneath the earth's crust. In fact, a small invisible and often fantastic universe exists beneath our feet. In these "twenty thousand leagues underground" Ulisse will explore the world of caves, observing speleologists in their explorations and visiting surprising sites such as the Wieliczka rock salt mine in Poland. Alberto Angela visited the depths of this mine which has been exploited for millennia and which today presents incredible settings: enormous caves, statues carved in salt, a church and even a concert hall with immense chandeliers all made with salt.