Hike up Huayna Picchu
The famous green peak which serves as a backdrop to Machu Picchu in thousands of photos around the world harbours its own hidden temples - including an arrow-shaped stone which points due south, and the Temple of the Moon, carved into a cave on the mountainside, which is believed to have been a royal tomb or possibly a place of sacrifice.
As you would expect, ascending the mountain is onerous, with exposed steps winding round sheer faces. The climb takes around two hours, and should not be attempted by anyone with vertigo. New regulations only give permits to 400 visitors, who climb in two morning shifts, so you need to arrive at Machu Picchu early to secure your spot on the "young peak".