Once you're in the country, getting to this site is amazingly easy. You just drive and park
I didn't pay admission either, because it's Friday. It's a UNESCO site, but there are very few restrictions for going. But they do have people watching, in case you do something like sit on a statue base, like I did (I was told it was perfectly OK, until some fellow in a watchtower used a bullhorn to tell me to get the hell off. Still I got my 2 pictures
).
US citizens can go though, I met a few on the way (you just need a letter of invitation from a tour company or someone living in the country, and you use that to get your visa). I saw tourists from all over the world, including EU countries and Japan. Overall I had fun, except for the poor air quality in the big cities (bad smog problem).