Okay, here's why so many people are denying the Cow Level.
The Cow Level is only available through battle.net. You can't get it at home.
If any of your characters has any hacked/duped items. or EVER did have ANY of them, you'll never get to the Cow Level.
If you have ever collected an ear, you'll never see the Cow Level.
Think of the Cow Level as Nirvana for purists, the people the play the game it was mean to be.
The prepubescent intellectually challenged who have done some of the above will never see the Cow Level.
The modification is made as an entry to the boot sector by Blizzard ... so you need to low level format your drive to ever trick the game once you've done these things.
To get to the cow level, download "The Ultimate Cow Level Extractor" It makes a white portal by the cows in town which then leads you to the cow level where you fight evil cow lords and try to gain Sacred Cow Power. Upon completing this level, by defeating the Chaos Cow boss, you will receive the ultimate prize...that's right Diablo Plate!!! The stats on this spectacular armor are +666 AC, +100 all attributes, resis all +75%, 800 durability. So, don't hesitate, go get The Ultimate Cow Level Extractor for an experience that you'll never forget!
The "Cow Level" reminds me of "The Castle in the Mountain" in the 1980 Atari arcade game Battlezone. Remember the volcanic mountains that served as a backdrop for the game? No matter how long/far you drove they'd never get any closer.
Well, rumors abounded that you COULD eventually drive your tank to the base of one of the mountains. Later, it was rumored that you could even drive up the mountain/volcano and look down the crater to find a CASTLE!
Ed Rotberg, co-creator/programmer of Battlezone, finally put an end to all the hyperbole when the PC emulated version was release by saying, "...And he [a Battlezone fan] said that inside the crater there was a castle, and that you could go inside and explore the castle. Of course, none of this was true..."
It goes to show just how good of a game Diablo is - and Battlezone was. I really think some gamers actually envision the cow level to such an extent they believe it's real! I remember huddling around Battlezone with friends for hours saying, "I think I saw them [the mountains] getting closer that time. Just one more quarter!"
One final note. Some seem to suggest that there MUST be a cow level because there WERE cows put in the game. Well, why not a rock, hut, river, tombstone, or grass level? Ok, ok - So the cows do talk/moo back to you...Why not a Wirt level then? I think you get my point. The cows are there because some programmer at Blizzard (just like some programmer at Atari for Battlezone) said, "Let's put some cows or chickens in this village to make it more like a village..."
Well, I've ranted and raved for far too long so I guess I'll leave you alone now. When you do get to the cow level, though, remember to take your...er...uh...I mean...My God, what have I done!...uh...MILK IT DOES A BODY GOOD!
You can get the map of the stars by hacking the Diablo CD or just going on to Battle Net and asking around. Someone will give it to you eventually. As far as getting into the Cow Level, here's how you do it.
Go out to the cows and stand between the two cows closest to the entrance to the Catacombs. View the map and drop it on the ground between the two cows. Going clockwise first go around the cow to the right and walk a figure eight pattern around the cows making sure to walk across the map as you cross between the cows. If you are not walking across the map you need to pick it up and drop it again so that you will walk across it.
Do the figure eight around the cows seventeen times. The way to remember this is that the Cow Level is considered level seventeen. After you finish the 17 figure eights pick up the map and go down to the church. Do not move inside the church. As soon as your character appears in the church, immediately click on up to town. It is very important that you do not move in the church.
Go back to the cows and repeat the procedure, this time after the 17 figure eights go down to the cats. Go back up repeat 17 figure eights and go down to caves. Do this one more time but go down to hell.
When you come up from hell view the map drop it between the cows and the map will become a portal to the cow level. Good Luck down there it is really tough. A level 50 character will have a very hard time in the Cow Level.
Blizzard has temporarily closed the cow level for renovations necessary to make it compatible with Diablo 2. Reportedly, the cow level will be the only way for your Diablo 1 character to access the world of Diablo 2, so it will be important to know how to get in. Among the reputed renovations for the Cow Level:
The Diablo cow level has absolutely nothing to do with the lame cowquest in Hellfire. Once you've seen the splendour of the cow level, you will know that there is no level, but the cow level, and I'm it's cow-tele-evangelist.
Many posters have brought up methods of getting to the cow level, and while some indubitably work better than others, the best way of getting there is as follows:
Equip a Plate of Trouble (any AC), or the Scavenger's Carapace (un-ided) and a Ring of Atrophy, obtain the milking stool from Adria, and go milk the cows. If you are good at it, eventually each of the cows gives you a quest. Once the First Cow has given you a quest you can go below (another tectonic fault opens up behind Wirt - you will hear a loud splash from the giant milk cauldron as Wirt falls in)
Make sure not to follow up on the quest the Third Cow gives you or you'll end up in a whole lot of trouble.
Be prepared for the fact that this is the most difficult part of Diablo and you will die a lot. Bring a lot of res scrolls and milk buckets.