I believe the route you're supposed to take is via the Underworld and the Abyss. The entrance to the Underworld is in Trammel on the Isle of Fire below a new volcano that has risen out of the water on the NW side of the island (no existing housing is affected).
Inside the Underworld is an entrance to the Abyss that lands you on the far "left" (for lack of a better description) end of the Abyss. If you stick to the "upper" half of the Abyss and work your way to the right, you eventually go through the center point of the Abyss, run like heck away from the Slasher of Veils, and then wind your way through the "right" end of the Abyss. At the topmost end of the Abyss is an exit. You emerge from the Abyss at the far end of the Tomb of Kings.
As of last night, when you emerge from the Abyss into the Tomb of Kings, you can't go any further past the Guardians, unless you happen to be on a quest that I believe starts on the Ter Mur side of things. Haha.
So for now just use the shortcut moongates scattered on Retribution during the testing phase.
As I was running though the Abyss last night, I also found what looks like it may be another entrance, but I don't know where it comes from. It's location 3 in the series of screen shots I did on the Abyss last night (
http://vboards.stratics.com/showthread.php?t=153596). That thread also shows where you start out in the Abyss from the Underworld (location 1) and where you leave (location 42), as well as a shot of where you emerge in the Tomb of Kings (screen shot 43).