We've got Foamhenge here in VA. Full scale replica made of styrofoam. Built as an April Fool's prank, and just left there on the hill. My favorite part is the sign explaining the history of Stonehenge and that in was built over hundreds of years using thousands of laborers. It then goes on to say that Foamhenge was built in three weeks by three mexicans and one crazy white guy.

The bike, coincidentally enough is for sale, but the admission to foamhenge is free!