In every instance of the Cow Level there is one unique Hell Bovine named 'The Cow King' who drops some rare loot.

The level is relatively small, a repeating wilderness area full of 'Hell Bovines', cows that stand on their hind legs and wield large polearms or battle-axes while mooing angrily at the player. This level is accessible in both the standard game and the expansion, Diablo II: Lord of Destruction, but only once Diablo has been defeated. This will open a red portal in the Act I Rogue Encampment, which will teleport the player to the Secret Cow Level. In Diablo II the cow level is at last a reality accessible only by combining Wirt's Leg, the peg leg of Wirt (a resident of Tristram in Diablo) and a Tome of Town Portal in the Horadric Cube. Eventually the name got mixed up in the myth itself, and people said that the Cow Level contained cattle-themed versions of all the game's enemies, such as acid spitters which sprayed milk on the player, or Goatmen who were actually Bullmen, all led by the Cow King, an ultra-powerful boss said to be stronger than Diablo himself. The 'Secret Cow Level' as it was referred to, was said to have the most powerful weapons in the game and super-powerful adversaries to use them on.

Some said players had to open a scroll of town portal, some said that players had to poke them (to initiate dialogue) hundreds of times, there were multiple variations on the theme.

Specifically, that there was a super-secret level players could only reach by doing something to the harmless cows in the town of Tristram. Once upon a time, a popular, yet entirely untrue rumor popped up concerning Blizzard Entertainment's seminal hack-n-slash RPG, Diablo.

How to get to secret cow level diablo 2