How to get to The Void (CoTF)
The Call of the Forsaken version of The Void is reached by taking the portal in the northeastern most portion of Ethernere: Tainted West Karana. In the little hub of portals there will be a portal to The Void, take that and you'll be able to complete your traveler achievement for that zone.
Going to The Void (SoD version) will not complete your CoTF traveler achievement. If you're looking for how to get to that version of The Void instead then follow the link provided to be taken to my guide.