The Metro reports that over-tourism has been a growing problem for Machu Picchu, which has caused UNESCO to step in and request more be done to limit the amount of allotted visitors at a given time.
Of course, there are ways to get around the masses. Although a rugged adventurer may be less excited by the prospect of a train ride, the rail route to Machu Picchu provides trekkers with rarely seen sights. Travelers will catch glimpses of glaciers on Mount Chicon and Mount Veronica that most humans will never behold, while the vistas of the Amazon from a rail car are unique as well.
While Machu Picchu is awe inspiring year-round, travelers really looking to avoid the massive crowds can plan for a late spring trip, as May is a prime time to go for both good weather and least amount of tourists.