"Ghost Town" was the name given to a place in GTA III, a "hidden" place, not avaiable in a normal game play. This place was used by the game for the introduction to the story. It's basically a street with a bank (the Liberty City Bank, if I'm right), where the hero of the game is shooted down during a robery. This place could be available only trought a patch (on the PC version) or by plane (with the Dodo), in PC and PS2 versions of the game, and it's not landable (except, once again, with a patch on the PC version).
And, no "ghost town" isn't haunted, nor full of secrets/mysteries... (: