Landmarks--USA vs. the rest of the world?

I have traveled in Europe extensively and must say that they have some magnificent sights. But I think a lot of that is due to the length of history they have behind them. The US is a relatively young country and considering that most of Europe has been around for a long time, the US holds her own. If a person never ventures out of our countries borders, they will have a lifetime of exploring to do and STILL never see all that this great country has to offer.