re: Does it blow anyone's mind the Twin Towers of the WTC aren't there anymore?

I think there's only one building (or series in this case) that I can say with reasonable confidence will still be up in a thousand years, and they're the Pyramids. They'll be buried before they're destroyed. Mankind's most durable building is also one of its most ancient. That and some impressive dams. Other than that, most structures are far too hollow, metallic, or wooden to hold up for more than say 300 years without significant constant repair.