One of the best-kept secrets in Blizzard's Diablo. Once you found the cow level, you would find yourself attacked by cows with polearms.

Supposedly just an April Fool's joke by Blizzard.

The cow level was the long running joke in Diablo 1 about a secret level filled with cows. It is a reality in Diablo 2, much to everyone's surprise.

To get to the level, you have to finish the game at least once and use the horadric cube to combine wirt's leg and a tome of town portal. A red portal then opens taking you to the cow-packed level.