A tremendous aberration in the cosmology of the timelines, and a great consternation to any aspiring cosmographers, the Grand Ex are a pair of time-space planes with one intersecting line. Each of these time-space planes has dozens if not hundreds of alternate timelines, which are difficult enough to map. And one of these alternate timelines, but only one, is an alternate for both worlds. This would be a convenient short cut for any travelers wanting to travel from one world to the other, but unfortunately travel between the two worlds is strictly watched and monitored. There is only one gateway between them, and it is rarely seen or used.