This is the one for wonder that you can’t actually see.  But there’s this lovely plaque commemorating them.

Did you know that the shoreline of San Francisco used to be a lot smaller?  The whole Embarcadero is landfill.  And what do you do with broken-down ships?  Leave them where they are and fill in around them.  I love the idea that when I’m walking down by the water, there are ships under my feet.