I know I mentioned on Facebook that I would make a post a while ago. Alas that didn't happen and I never got around to it until now. On the plus side I am now using MarsEdit 3.
Underground cities which are connected by a subway system. With huge stretches of uninhabitable land between cities the only way to get between them is the ancient subway system. Small stores have been constructed around the stations selling everything a tired traveler might need and anything an eager visitor could imagine.
People wait expectantly for their loved ones to arrive or work frantically to earn enough money for a ticket to leave there boring home and see what else the work might have to offer.