It’s gloomy, depressing and ridden with tangled, clawing roots. The Shivering Isles is the embodiment of the mad prince’s bipolar personality: Mania is a land of bright colours, weird flora and even odder fauna Dementia, on the other hand, is dark both visually and psychologically.
Adventurers are held here, prevented from entering the Shivering Isles proper by a monstrous gatekeeper that holds the keys to the twin realms Mania and Dementia. After a chat with Haskill, chamberlain to the Daedric Prince, you’re unleashed into a kind of purgatory, replete with giant mushroom trees and odd characters. After the prerequisite “story setup” encounter with a knight outside this portal, you can step through into the realm of Sheogorath, Daedric Prince of Madness, much as you do when entering an Oblivion Gate.