The Darkness beneath Azeroth: The Titan's Tartarus
My theory is about how the "Darkness" Sylvannas saw chibi-Arthas after she was killed, Malfurion sensed beneath the waves, and Ra'den speaks of may be related a to a Netherworld. It makes me wonder if this is what Blizzard is leaning toward.
And if it was Titan created how cool would it be if it was am underworld like Tartarus for the Titans. A prison or realm that the Titans sent the worst of the Worst to suffer, even fallen Titans (Not necessarily Sargeras but I would'nt leave him out.
--->> Puts on Tin Foil Hat
In her story Sylvannas meets the lost 6 year old version of Arthas doomed to wander for eternity in a realm of eternal darkness. She also is warned that this dark realm is a REAL place that apparently is thirsty for souls like hers when she died from a bullet to the head the Vry'kul again pull her from this "Darkness" when she is killed.
The "Darkness" is constantly being felt by those with great power. Malfurion felt it from the Abyss at the bottom of the ocean. Ra-den knows what it is beneath Azeroth but "dares not speak its name." The Old Gods have been clearly named in Ulduar by by the keepers so why would Ra-den, Wrathion and everyone else keep this place a secret.
The tomb of Sargeras where Gul'dan met his headless end in WC3 has since slipped beneath the waves. Whatever killed him is still down there. Waiting... only slightly undectected until the Cataclysm that tore open Azeroth.
Hmm, I myself like the idea of a titan version of the Arcatraz... but them creating an actual dimension to hold negative energy is even better! After all, they can create the Dream and the Elemental Plane, why not a hell. And if the Old Gods have begun infesting the other realms, and the titans imprisoned an Old God in this Tartagus... urg, I'd hate to see the place now.
A whole pack of fallen titans sounds pretty bad too.