Huaynu Picchu is the large, sugarloaf type mountain seen in those familiar photos of the mystic city. Travelers are certainly able to climb to the peak, but some arrangements need to be made in advance. Whenever you take a tour to Machu Picchu, make sure to get your entrance tickets in advance, since the number of tickets issued each day is limited. If you do want to climb Huaynu Picchu, you will need to specify that in your reservation and pay a small extra fee.
Only 400 hikers are permitted to Huaynu Picchu every day and they are divided into 2 groups. The first group can depart between 7 and 8 a.m., the other group may depart between 10 and 11 am. The hike is strenuous, and in some places, treacherous. In all seriousness, there are places where one false step may result in a fall of several hundred feet or more. There are steep cliffs, caves, and very steep stairs to deal with at various points. However, the view is absolutely, positively spectacular.
It takes about 2-3 hours to do the round trip hike.
The Sun Gate goes along the Inca Trail, ascending gradually about 1,000 feet or so. It is a much less challenging hike than Huaynu Picchu, but not much less spectacular. It too, is about 2-3 hours round trip.