I have seen a lot of videos showing places that are not intended to be explored, even if people manage to enter them exploiting glitches of the game. I like in particular Old Ironforge, and the sense of mystery that someone can fell while discovering, maybe back in the first version of WoW, that undiscovered hiding.
With the coming of Cataclysm and the Archeology profession, along with the terrain phasing technology, it would be very interesting introducing - intentionally - in the game a handful of places which are hard to discover, or even to reach. Those hidden areas would contain some strong mob to fight - alone - or a chest, or a legendary artifact (those artifacts available with Archeology, not an item of insuperable quality). They would be, perhaps, discoverable in certain period of the day, of the week or of the year, or there would be only one chance to find them and after this they will disappear from the world.
Those which have been glitches could become an interesting part of the game, revaluating the feeling of exploration. Becuase WoW has one of the largest environment I have ever seen; there are hundreds or even thousand of caves, hidings, fortresses, castles, submerged areas and so on. They could possibly make a kind of treasure hunting, hiding pieces of a map in some chests spread along all the world, from the luxuriant jungle of Stranglethorn to the chilling peaks of Storm Peaks, from the infected lands of Shadowmoon Valley to the sand-covered terrains of Silithus and Tanaris...
What do you think of this idea?