A secret level in the popular game Diablo 2. You morph tome of town portal and Wirt's leg to get a portal to it. This started as a rumor in the original Diablo, but was quelled when Blizzard wrote a cheat for Starcraft: There is no cow level. entering this cheat provided instant victory. it was added in D2. It features weak monsters that give out a lot of XP and rarities.
Like that battle staff? I got it on a cow level run.