Wolverine Origins Easter Egg - Warcraft 3 Arthus and Frostmourne

After you get the adamantium coating on your skeleton and leave the weapon x facility grounds for the first time, run toward the woods using your feral sense. Keep running toward your next goal, but keep an eye out toward the right and you will see a blue object hidden in a crack in the ice. The crack is big enough to run into.
Go in and you will see the skeleton of Arthus lying inside next to the frostmourne sword from warcraft 3.
If you are playing on a X-Box 360 an achievment will unlock called "WoW."
This was done by Activision to make it clear that they have joined Blizzard studios.
This is well hidden, and this is a secret achievement for the game that is not listed on the achievement list.