It's no wonder Machu Picchu is Peru's most-visited site. Dating to the mid-1400s, it's a marvel of mortar-free limestone architecture perched on a high plateau deep in the Amazonian jungle. Get there via train from Cusco or, if you're not faint-hearted, make the trip on foot via a multi-day hiking trail—you'll travel through deep Andean gullies and enjoy stunning views.