Machu Picchu
Yes it's very touristy and yes they take every opportunity to fleece you out of as much money as possible (10 times the normal price if you want to buy a bottle of water at the site!) but the scale and location of the site really is incredible. It's the first site that has really come close to matching our visit to the Angkor temples in Cambodia.
We arrived at the site really early so it was pretty misty to start with but an invigorating climb up Huayna Picchu helped clear the cobwebs while the mist also cleared. The train ride both ways would have been pretty impressive had it not been for travelling backwards both times or having to listen to inane drivel both times from the guys sat opposite!!!
Afterwards we returned to Cusco for a couple of days which is a nice little town if a little touristy being the gateway to Machu Picchu. We then headed down to Puno where we today spent some time on Lake Titikaka (photos to be posted soon) visiting the floating reed villages and other islands still inhabited by indigenous peoples.
Tomorrow we jump back on the bus and head down into Bolivia. First stop, and hopefully a chilled one, is at Copacabana, still on Lake Titikaka.