I loved the Salkantay trek. We arrived two days before we got on the trek and so we were a little scared about altitude sickness (we are from Holland and live below sea level) but were totally fine. Our guide was very good (good tips about culture, nature, etc.) and positive what made it fun and relatively easygoing.
Highlights of the trip were the lake (at 4200 meters and was very impressive) we visited the first day, the pass of Salkantay Mountain the second day (it felt really good to reach the 4600 meters high point which was spectacular), the rainforest (the green was overwhelming), the third day, the hot springs, the fourth day (fine moment to relax) and the absolutely highlights was of course visiting Machu Picchu.
Highly recommend this trek. You should definitely try it !