A random, but possibly neat idea seed for a game (I think it would work especially well at a convention):
The PCs are divided into two groups before the game actually starts, and the two groups are essentially exploring the same area (though they start in distinctly different places in the area). The "kicker" I guess is that one group is there some period of time after the other group. Really I just like the meta aspect of discovering that the other people at the table are exploring the same place, just either before or after their group. I don't really know what else you would do, it just seemed it would be fun to realize halfway through that you aren't going to run into these other characters...
If someone figures out a cool scenario somewhat like this, let me know, I'd love to see how it would play out...