The hike from the Machu Picchu ruins  to the summit of Huayna Picchu (elevation 2,740 meters, or 290 meters above Machu Picchu) is a moderate two-hour walk, and approximately 1.9 kilometers round-trip. It starts at the Sacred Rock  and passes through a gate that is open 7 a.m.–1 p.m.
Only 400 adults a day are allowed to do this climb (children are not allowed). Arrive early if you want to climb Huayna Picchu. It may make sense to climb Huayna Picchu in the morning and then see the ruins afternoon, in order to avoid missing this hike.
While it is steep, the path is in excellent shape, though the last 20 meters include a steep rock slab that must be climbed with a ladder and a rope.
The Inca built retaining terraces, buildings, tunnels, staircases, and a shrine on the top of the mountain. Human remains were also found in caves. The splendor of Huayna Picchu is the breathtaking view of the entire complex, which spreads out before the summit like a map.
Farther down on the slopes of Huayna Picchu is the Temple of the Moon, a construction equally as exquisite as the Temple of the Sun but with an entirely different mood. The easiest way to visit the Temple of the Moon is to retrace your steps down from Huayna Picchu and take the marked trail turnoff halfway down, which leads directly to the site.
There is also a very steep and technically challenging trail that descends from behind the summit of Huayna Picchu itself. This trail, which can be hard to find, contains a short but near-vertical section climbed with a lashed wooden ladder.
Visiting the Temple of the Moon adds about 1–2 hours onto the Huayna Picchu hike. If you visit both Huayna Picchu and the Temple of the Moon, expect to spend about 3–4 hours, so take plenty of water and food.
The Temple of the Moon is a medium-sized natural cave where rocks have been fitted perfectly in flowing, gentle shapes. Instead of the tower and bright sunlight of the Temple of the Sun , everything here is recessed and dark, with sinuous lines.
The Temple of the Moon itself is a wall of doors and windows sculpted perfectly into the space created by a giant overhanging rock. A bit below there is a doorway that leads to other structures, including a lower cave that is near to where the trail from Huayna Picchu descends.
The Temple of the Moon is wonderful in part because few people ever visit it. The spiritual energy of the place is palpable.