Relics of ancient civilizations like Stonehenge, the giant head statues [Moai] on Easter Island, the Pyramids, etc, are wonders of the world.
There are standing stone circles all over Europe. Why were they built, how were they built, we still don't know. Those people didn't even have metal tools! How did they lift the pyramid stones?
I have seen and walked through acres of fields of pyramids deep in Tulum, Mexico and when you view these ruins you feel a solemn sense of ‘time’ and awe and think about the people who once walked there.
Carhenge, in Nebraska and Cadillac Ranch in Amarillo, Texas are curiosities to give a laugh. Like the local WalMart, we know when, why and how they were built.
http://www.roadsideamerica.com/attract/images/tx/TXAMAcaddy1.jpg
Remember the scene of the Statue of Liberty sunk in the sand in Planet of the Apes? That would be a relic of ‘us’.
These are NOT my pictures but show many scenes from the Mayan ruins in Tulum. They are much larger and impressive than the pictures show;
http://www.tequilarista.org/images/Mex_Vacation_2003/Mex_Vacation_2003.html
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Good comments potlatch

Nice post, potlatch.
I’ve been to Tulum.
Those ruins are amazing!
Have you been to Chichen Itza?
It’s now one of the seven wonders of the world.
We enjoyed our visit there so much the first time that we returned before we had to leave Mexico.
There’s a lovely little city on the way to CI to have lunch called Villadolid.
http://en.wikipedia.org/wiki/Valladolid,_Yucat%C3%A1n
They even had an internet cafe. ;o)