Speed Limit 25
Bunker Hill Road Tunnel
This tunnel runs underneath highway 101, just north of the Golden Gate Bridge, and connects Sausalito to the Marin Headlands. I once rode my bike through this tunnel when the lights were out. It was pitch black and all you could see was the light at the other end, which looked very tiny because the tunnel is about a half mile long. I could not see the road or even my hands on the handlebar. It was very eerie and the end of the tunnel couldn't come soon enough.
Here's a lower, centered perspective, slightly farther into tunnel, in color: www.flickr.com/photos/brandondoran/5432501861