You might find it hard to believe that bleak, wet, and windy Potosí was once one of the richest cities in the world. It's been said that enough silver was pulled from the bowels of nearby Cerro Rico to build a bridge from Potosí all the way to Madrid -- and enough people died inside the mines to build a bridge of bones all the way back.

Nowadays, visitors can still see the two disparate sides of the city. Seven thousand workers still eke out a living from a mine where millions died. You can take tours there that'll bring you face to face with these miners and the dreary conditions in which they work. In contrast, you can then tour the sights that evoke the city's former glory. Potosí is not a heartwarming place. At more than 3,900m (12,800 ft.), it's one of the highest cities in the world. Even when the sun is shining bright, there is always a bitter chill in the air. It's painful to visit the mines and learn about the past exploitation of these workers, but it's also fascinating to see the remains of a place that was once the home of some of the wealthiest people in the world.