EASY achievement. Go to Darkshore and jump into Maw of the Void, found around 53,31. You’ll see a short cinematic of yourself being sucked into the void then fall into a hidden underground cave….
You’ll see Bielary Ivy Shroud, an NPC who can transport you back out but DON’T leave yet. Go up the ramp, kill the two low level ghosts. At the top of the ramp stands Telarius Voidstrider. Kill him and he’ll drop “Wrigints of the Dark Herald” which starts a quest. On clicking the quest item it will turn into “Writings of the Void.” Take this to Ranger Glynda Nal’Shea and on turn in you get the achievement “Ghosts In The Dark.”