We still don't know exactly what led the Incas to abandon Machu Picchu all those centuries ago, but there are plenty of people clamoring to hang out there these days. The grand and mysterious citadel, which was built in circa 1450 during the height of the Incan Empire, receives at least 1 million visitors annually, making it one of the most popular travel destinations in the world.
Sadly, this special place has become a victim of its own success. The large volume of visitors raises serious questions about the amount of stress the ruins can withstand, and there have been several battles over the commercialization of the area.
In hopes of lessening the impact posed by tourists, the officials have deemed Machu Picchi a no-fly zone and instituted limits on the number of people who may visit the ruins each day. Additionally, UNESCO has considered adding Machu Picchu to its list of endangered World Heritage Sites.