I've seen the Eiffel tower from a large distance (from the highway near Charles de Gaulle IIRC), and Stonehenge also from the highway. So that's not a lot
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However, there are many very impressive structures. When I first entered the (still unfinished atm) renewed Antwerp Central Station I said to my SO: "it doesn't hurt people when they build something slightly over the top from time to time". And that's the feeling I get with anything that IMO would form a candidate for "wonder of the world": something really impressive, more than strictly necessary or than the easiest solution, something that makes you think about the effort/creativity it cost to create it and/or design it and makes you proud that humans created this.
I can't really pick 7 from the 21 candidates, never mind from every candidate I could come up with.