Using a greeting card with a small LCD and GPS, have a button that you press that only displays how far you are from the meet-up. Thus, a meeting organizer can set up an unknown location where the attendees have to zero in on a location by trial and error.
It could also be accomplished with cell-phones...and probably best over distances that can be walked since I wouldn't want car crashes due to figuring out where to go.-- toodles, Jun 21 2010 Reverse Geocache puzzle http://hackaday.com...zle-gets-downsized/ [toodles, Jun 21 2010] Fireball Run Road Rally http://fireballrun.com/index.phpOne of the Grand-Daddy of all Road Rally competitions, with an eight-day cross-country course and parties in every destination city along the way. [jurist, Jun 21 2010] Long before the days of GPS we used to play a variation on this game with Road Rally games where participants would congregate at a starting point. There they would be given a set of directions containing puzzle clues which would lead them to their next check point, where they would receive a new set of directions. Participants would leave at staged intervals to avoid "coat-tailing". The winner would be the the participant who arrives at the final destination closest to the exact elapsed course time if all the clues have been properly deciphered, checkpoints passed, and speed limits observed. When all the participants finally arrive at the ultimate mystery destination the party kicks in. [link]-- jurist, Jun 21 2010 random, halfbakery