According to FoundSF, there are many ships buried under San Francisco:
During the height of the gold excitement, there were at least five hundred ships stranded in the harbor, some without even a watchman on board, and none with a crew sufficiently large to work her. Many of these vessels never sailed again. Some rotted away and sank at their moorings. (Herbert Asbury in "The Barbary Coast")
This would be super cool to investigate! Are any of these buried ships open to the public?