Cross that bridge achievement
Take this achievement when you reach the day's coordinates while supported by a bridge or bridgelike structure. The bridge can be a highway overpass, suspension bridge, footbridge, or log across a stream, but the bridge must have been there before the coordinates were made public. If you build the bridge yourself in order to reach the geohash, take the MacGyver Achievement instead. The bridge need not cross water, but must actually span something, not just be a dike or other raised or narrow thoroughfare. The bridge must connect two places not simply jut out over water, so a jetty or diving board, despite being very cool, does not qualify.
Reaching the Point
It is not necessary to cross the bridge all the way when you come to it: it is acceptable to go only as far along the bridge as is necessary to reach the geohash, but the geohash coordinates must be reached while on the bridge. Geohashes that fall past the railings of the bridge are somewhat sad, but do not count for this achievement. Please note that some bridges are covered by anti-loitering laws, and that loitering on a bridge may attract unwanted attention, so try not to look too depressed if the GPS will not zero at the edge of the bridge. Geohashers who fall past the railings would be extremely sad, so please stay on the bridge.
If the bridge is low enough and the waters hospitable enough that jumping off the bridge into the water is safe and legal, then by all means take that route for an ordinary Water Geohash. Clinging to the underside of a bridge also qualifies you for the bridge geohash.
Your proof of location photographs should include a shot that shows enough of the structure or railings to establish that you are on a bridge.