Gundrak is a Wrath of the Lich King troll dungeon in the north of Zul’Drak, in Northrend. As a gold farm it’s a quick solo skinning run: clear the dungeon, skin every beast you kill along the way, and sell the leather, with a little raw gold from the trash on top.
A full clear takes around 4 to 5 minutes on a max-level character. Bring Skinning, since most of the value is materials, and look out for Arctic Fur, a rare skinning drop. Clearing only up to the second boss is quicker, but earns noticeably less per hour.
