What Lies Beneath: Salt has sustained this 13th-century salt mine turned museum, concert hall, and spa. Grandiose salt chandeliers with 300 burning candles cast shadows on a life-size rock-salt sculpture of Pope John Paul II and a wall carving of da Vinci’s The Last Supper.
How Did It Get There: Beginning in the Middle Ages, residents of Wieliczka, Poland, realized that a local natural resource, salt, could be a profitable commodity. During its working years, many lives were spent 1,072 feet below the surface in the mine’s 186-mile-long tunnels.
Cool Bonus: Tours of the mine began in the 14th century. A guest book, which is still used today, includes the signatures of Copernicus, Goethe, and President George H. W. Bush.