I liked most the beautiful spaces and how the buildings were designed to blend into those spaces. Very natural. It's like nothing I've seen elsewhere. The entire site is what I would show someone, while making sure enough time was set aside to enjoy it in a relaxed way, rather than rushing around as so many do.
I'd rest the night before and get accustomed to the height (8,000 ft) and catch an early bus up the hill to see Machu Picchu at sunrise, before the heavy crowds arrive.
The mountains might be covered by mist, which is itself an interesting sight there, but it normally clears and the sun coming through the clouds onto that site is something not to miss.
The entire site is interesting if you have a guidebook with you (they're sold there) or a guide. The site is very varied and the vistas are beyond gorgeous. If you understand the relationships of the various sectors there (or theories about them based on how the various buildings were built and arranged), you'll get more out of it. The 3 dimensional space of Machu Picchu, and how the buildings fit into the awesome surroundings, is what fills some of us with awe there. Take a lot of time to absorb the various nooks and crannies and different views from each.
My PhotoDiary of Machu Picchu at http://andrys.com/peru-25.html
explains the layout of the site and some of the theories of its use.
To see a photos-only page with captions that explain the layout also, I made another page at http://www.pbase.com/andrys/machu
You'll see why you shouldn't rush through the place, as it won't be as interesting without knowing some of its history and what the various buildings likely were and why they are made the way they are. I had a small guidebook with me, and the place is a little like a maze without one.
Some will want to climb HuaynaPicchu (the peak you usually see in the photos) but you need to get there early (and be used to uphill hiking) so you have enough time to get back down without rushing. I didn't do it but the views from there are astounding, from photos I've seen.
I loved being able to see the site after most people had left and before most people were on the site. We were staying at the now-expensive Sanctuary hotel up there, but staying just below the site means you can catch a bus up to Machu Picchu very early in the morning and see it before too many people flood the site. Bring good shoes, in case of rain, of course, if you go during November through April. May through October are the milder, sunnier months.
Take time to get acclimated to the heights there - about 8,000 ft. high, so it's very good to arrive in that area at least one night before and rest up before enjoying the site.
I've seen a lot of the world, but just being there in that gorgeous space is probably my favorite travel experience. Of course, people vary in what they like :-) But my PhotoDiary should give a good idea of what to expect.
Fondest memory: I loved most the sense of naturalness there and the beautiful spaces and configuration of the mountains surrounding Machu Picchu.
Favorite thing: If you w ake up in the morning and it's raining, or it's cloudy, do not worry... Aguas Caliente and Machu Picchu are part of a cloud forest, so it rains on and off. In fact, I found the clouds bringing some sort of mystery to the ambiance on top of the mountain. Make sure you have good rain gear and bring a rain poncho wherever you are going.
Favorite thing: You will read in a lot of tour books that say that it is quite difficult to get a picture of the entire site of Machu Picchu without special lenses, but that isn't quite true. One of the best ways is to climb Huayna Picchu on a clear day and take a picture from there, but if you don't feel like climbing the zillion stairs to get to the top of Huayna Picchu or you just aren't fit enough, there is a great location on the actual site of Machu Picchu where you can take great pics of the majority of the site. If you climb near the Guardian's Hut and onto the Funerary Rock, you can take great pics of Machu Picchu.
Favorite thing: We read several times that it is impossible to take a bad photo of Machu Picchu. Well, since we took over 400 pictures, I'm sure that the adage is false. However, Machu Picchu provides the opportunity to takle some really beautiful photos just by using the ruins themselves. Frame the mountain scenary with a window. Use a door to outline some llamas. You will be impressed just how good your pictures look.
Favorite thing: this is still on the way to Machu Picchu. On the photo you see a view down to the ground of the valley where the river Urubamba goes its way and next to it the train from Cusco to Aguas Calientes and further on through the valley passes by.
puerta del sol.... near the sunset.... incredible view.... incredible light.... breathtaking.... and.... after all the.... stairs... steep... stairs... you'vegot.... to... climb to.... reach the gate.... a breathtaking thing.... can kill you.... this is how you'll probably speak and what you probably say about it... when you arrive at the end of the path you see the stairs, in the dark ... it's not a long step but you don't know it yet.... really really steep steps, and you're quite used of steep things when you walk till there
Fondest memory: the last step! you'we got a wall in front of you you need to slide a bit and that's it... you can only live it, not explain it!!!! no matter if you're expecting something, no matter you saw it hundreds of times in pictures, prints, movies, dreams.... I saw no one able to walk for a while after the view.!!!
well, maybe you're just tired....