Machu Picchu is an ancient city built by the Incas in the 1400s. Located in Peru on the top of an Andean mountain, it is completely self-contained and invisible from below. It appears to have been used for ceremonies and astronomical observatory.
From Sacred Sites:
Two thousand feet above the rumbling Urubamba river, the cloud shrouded ruins have palaces, baths, temples, storage rooms and some 150 houses, all in a remarkable state of preservation. These structures, carved from the gray granite of the mountain top are wonders of both architectural and aesthetic genius. Many of the building blocks weigh 50 tons or more yet are so precisely sculpted and fitted together with such exactitude that the mortarless joints will not permit the insertion of even a thin knife blade.