In the 16th century, Francisco Pizarro captured the Inca leader Atahualpa after he defeated his brother for the throne. The Inca offered a ransom of a room full of gold, but before their final and largest installment of the treasure, they found that Atahualpa had already been killed. Legend has it that they then buried it in a mountain cave.
Stories of treasure hunters seeking the lost gold abound. One Spaniard, Valverde, married an Indian woman about 50 years after Atahualpa's death. He became incredibly wealthy after his new family allegedly led him to the hidden treasure. He left written directions to the location with a detailed map of the area.
The legend subsided for hundreds of years, until Richard Spruce, a botanist who traveled to Ecuador to collect seeds from the cinchona tree (the source of quinine), found Valverde's map. Though there has been some speculation over whether the map was real or not, today's archaeologists believe that it's likely the map is authentic, but that the treasure - if still there - will never be found.
Since the late 19th century, many adventure seekers and treasure hunters have tried to find Atahualpa's ransom, and some have died on their quest. The last person who was thought to actually find the treasure was Barth Blake in 1886. He wrote that he found the gold, and that it was so abundant that even 1,000 men couldn't clear it out. He took what he could carry and went to New York, at which time he collected more money and a crew to go down and claim more gold. He was thrown overboard during the expedition.
It's hard to tell if there really is a hidden treasure. Unfortunately, the mountains it's said to be hidden in are prone to earthquakes and other natural disasters, so the treasure is likely lost forever.