Alright so many people have been wondering how to access R'lyeh portal and get to The Cow Kingdom (Inferno Cows). I'll be answering those questions and how to defeat the monsters inside here =D.
So to open R'lyeh you're going to need the 3 Azathoth organs (also known as blue organs) that can be found from any kind of special monster in Hell, these include the brain, the eye, and the heart. Once you have these put them inside your cube in act 1 and click transmute. Be warned, the mobs inside are very hard to defeat, but provide very good loot most of the time. The boss Avatar of Azathoth inside will drop a cache everytime that you can open with a Key of the Old Ones from Hadriel or by opening them at Cthulhu altar. Once you have navigated and completed R'lyeh, you will find the The Cow King's corpse next to where you fought Azathoth.
To open The Cow Kingdom portal, simply collect The Cow King's organs farmed from hell cows and these include, Brain, Eye, Horn, Heart, and Tail. ( Azathoth's organs can also be found in hell cows). Once you have all The Cow King's organs, you can stand over The Cow King's corpse and find a ! over your characters head, then take all 5 cow organs in cube and click transmute, this will open the portal to The Cow Kingdom.
Also be warned going in here if you are not geared high, as these cows are FAR stronger than hell cows!
Now for strategy, I built up a java zon using charged strike as main attack, im able to solo R'lyeh and inferno cows with relative ease. Necromancers also work very well due to Corpse Explosion.
I hope this helped answer some questions from the community and happy hunting everybody get that loot!