I've been to 16 of these particular ones, and many others in the U.S. and abroad that aren't listed, places in Asia, Europe, and Canada, among others, and quite a few in the U.S. not listed. Anyone ever taken the underground walking tour in Seattle? How about the red light district in Amsterdam? Hey, I wasn't a customer, just a tourist.
Pretty random list, I suppose you could come up with dozens of similar ones - I start thinking of places I've been that didn't make, it, lol, like where's Mammoth Cave? Mark Twain's boyhood home? Wrigley Field? Could go on and on, but fun to compare.
I've been to 10. Although I saw it from the car and from a battlement above, this is my favorite shot of the Golden Gate Bridge from a trip a couple summers ago. I'd say the ferry ride over and back from Sausalito and lunch at the Molinari delicatessen were the highlights of an entire day walking about San Francisco - it was fine, just won't be stopping when we drive through this summer. And when I get my notice to pay the toll for the bridge in the mail, I won't delay getting it paid!