Potosi is one of the highest cities in the world with an elevation over 4000m. I had a difficulty sleeping well there as I kept waking up gasping for air. This city was founded in 1545 as a mining town at the foot of a huge mountain filled with silver. About 41,000 metric tons of silver were mined there between the 16th and 18th century making the city one of the richest in the world. Some say about 20 million people died working in appallingly poor condition in the mountain over the years. Work continues to date and the current life expectancy of a miner is 40 years of age.