Diablo 2 Secret Cow Level Guide
The secret cow level is a secret portal that can only be made in the Rogue Encampment once you have completed the difficulty.
Its a red portal that can be made using the Horodric Cube and when you enter the portal, the only enemys are giant cows that hold axes and "moo"
Go to Tristram and get the 'Wirts Leg' from a corpse at the top section of the map.
Place the Wirts Leg in the Horodric Cube with a Tomb of Town Portal and click the button.
The portal is now open.
Do not kill the cow named 'The Cow King' because if you do, you will be unable to make the portal again in that difficulty.
If you are playing on Battle Net, other players in your party will also not be able to make the portal.
It is recommended that you leave the party if you want to kill The Cow King, as you cannot do runs on this map if no one in the game can create the portal :)
Have fun killing the cows!