If you want to get there you need to know the recipe for Horadric Cube to transmute ingredients and open the portal to the secret cow level. What you can expect from Diablo 2 cow level is a separate area where all monsters are the same cows, called Hell Bovines, with polearms and the background voices are also making the cows. It has become so popular that Blizzard decided to add it in Diablo II to make it real.
The Secret Cow Level once was a joke and rumour in Diablo I.
