Hellish Staff of Herding
From Diablo Wiki
The staff has only one use, to open a portal to the secret level Whimsyshire. Having this item in your inventory allows for you to access Hell Difficulty level.
This can be crafted after obtaining the plans for it from Gorell the Quartermaster in Bastion's Keep Stronghold. You must be in Act IV Hell Difficulty + have Prime Evil quest to buy this!
Gorell sells the plans for 50,000 gold.
This staff upgrades to the Infernal Staff of Herding.
Gorell the Quartermaster, Bastion's Keep.