Good Vibrations (of the slightly scary variety)

The Golden Gate Bridge is 8,981 feet across, and you really have to walk it to get a feel for how enormous it is.

When you do, the giant red structure, which seems more like artwork than engineering from afar, becomes a real working, moving, imperfect thing. You notice scratches and big dull spots in the "International Orange" paint. You hear the roar of traffic.

And, most of all, you feel the vibrations. The road is suspended from cables, and those cables vibrate "like piano strings," as one passer-by put it. No shock, really, since the bridge is built to handle 27.7 feet of sway in the case of an earthquake or disaster.

(some info for post came from National Geographic travel guide to San Fran ... which I highly recommend)