The hike was much tougher than I expected, but well worth it! Be prepared for hard hiking (LOTS of steps) as well as beautiful views.
You'll feel very accomplished once you walk through the Sun Gate and see Machu Picchu for the first time! Day one is fairly easy hiking. Day two, the tables turn and the hiking gets much harder. All uphill and high altitude. Bring coco leaves to help. Day three gets better, but be prepared to feel very tired and sore legs/feet.
All and all the experience is wonderful and I wouldnt do it differently. Definitely a must do!