Built in the 19th century, Sutro Baths in San Francisco were once part of a privately-owned swimming-pool complex. But after an unsuccessful run, the complex was abandoned and now lies in ruins.
The swimming pools were never fully removed, however, and visitors can freely walk around the surrounding area. These ruins offer a great view and make for some impressive pictures; the juxtaposition of the sea and the man-made pools is an interesting contrast. Sutro Baths are also a reminder of how powerful nature is, and how it can reclaim even the most impressive structures created by humans.
Be sure to explore each area of Sutro Baths, including the adjacent cave. Reaching the end of the cave will give you an impressive glimpse of the nearby water. There are also trails that lead to cool views of the Golden Gate Bridge — as if you needed another reason to go.