My favorite thing is San Francisco was the ruins of the Sutro Baths, a private swimming complex built in 1896, and incinerated in 1966. Set on a cliff over the Pacific Ocean, the sea has transformed what remains into the semblance of an ancient ruin.
I’m going to write more about it later, but in the meantime, here’s some footage of the interior produced by Thomas Edison in 1897. I want to go to there, and so, I think, should you.