Okay, weird question but I cannot remember what exactly it was.

I remember it being mentioned in game somewhere that there is something beneath the Shivering Isles that is "alive" and possibly spread throughout all of the underground of the realm. I can't remember the exact details but I think it had something to do with roots or whatever but that it was living and aware and that supposedly even Sheogorath knows little or nothing about it. In fact, I believe it was considered heretical to mention it.

What I'm saying above is kind of odd but that's because I don't remember the exact details. All I can recall is it made it sound like there's some monstrous being lying beneath the Isles and/or that the Isles may somehow be alive/aware as a result.

Hopefully one of you lore buffs don't think I'm nuts (ha! after all look at the realm we're talking about) and knows what I'm referring to.

Giant Crystals associated with Lord Jyggalag do exist under Mania and Dementia.

No, I don't think that's what I'm referring to. IIRC it was a reference to some continent (or island) spanning entity that existed beneath Shivering Isles. It's not something you ever actually see in game or anything. It's mentioned in one of the books or scrolls in-game.

I came across what I was looking for just now.

http://www.uesp.net/wiki/Lore:Bark_and_Sap