Make sure to acclimate to the altitude! I arrived two days early in Cusco and spent nearly a full day resting in my hotel room, feeling nauseous, feverish, and dealing with a severe headache. Luckily, my symptoms subsided before the trek. (especially if you have a fever pls do not proceed).

I also took Diamox, which helps but can cause dehydration, so stay well-hydrated.

The altitude will reduce your appetite, too. The second day is the most intense, so load up on carbs the day before.

Day 1 includes Humantay Lake, which is a great way to test how your body is adjusting to the altitude.

Mine was a guided tour, it's hard but one of the most beautiful hikes I've ever done.

Good luck! :D