I visited Peru in 2008 and got to go to Machu Picchu. It was amazing.
We arrived early in the morning and went straight past the ruins and up the mountain next to it. It was very foggy and cloudy and we could not see a thing down below. We waited for half an hour and slowly the fog lifted and the clouds parted. What a sight that was! The ancient city slowly revealed before our eyes, almost better than once it completely cleared up.
There are also ruins on top of the mountain to the right of the ruins (across from the ruins in the photo below); tiny, slippery stone stairs lead up there, a bit scary at time (especially on the way down), but totally worth the climb.