Tiahuanaco
Tiahuanaco was surprisingly un-touristy for one of Bolivia's major World Heritage Sites. When I turned up, considerably after the scheduled opening time, I had to wait for the staff to open up the ticket office - and then seemed to be one of the first few people entering the site in the morning.
It took some imagination to picture the site as it might originally have looked - some intriguing stone workings survived, but a lot of it was just earth mounds.