Guide: Getting into 'Development Hell' secret level
Thankfully, getting Development Hell to spawn is much easier than grinding the Staff of Herding materials and it took this writer about thirty minutes of his time. This is what you do:
Select "The Shattered Crown" / "Northwest Gate" quest and go to the Cemetery of the Forsaken
Some people have stated that this is indeed the optimal quest for the crypt to spawn and you need to be on nightmare difficulty or higher. Apparently, the secret level will not spawn on normal but this shouldn't be much of a problem - it's been 11 days since the game's launch and having nightmare unlocked should be withing anyone's reach.
Check out the Cemetery of the Forsaken for a fourth crypt
As you know, only three crypts usually spawn in that area. If the Development Hell crypt spawns, it'll be in addition to the other three. If you see a crypt missing, just remake the game until it appears.
Enter the crypt and kill everybody
If you are a Diablo III hater and want to hurt Jay Wilson for what he and his team did to your favorite franchise - that's your chance! Although I love Diablo III, I cannot bypass the chance to go hand-to-hand with the game director. Jay is big and hits hard but I am a super saiyan barbarian and my flames are stronger than him!
Oh, and I also got a sweet Feat of Strength achievement which I can use to irritate friends and colleagues and make them jealous.