It is, you see, the Realm of Madness itself, and the unlucky inhabitants find themselves permanently in the grip of insanity. Precisely which breed of psychosis it is that looms over the heads of its incumbents depends entirely on which part of the isles they originate from, as this is a land that’s split down the middle in two - both geographically and psychologically. A giant ridge runs straight through the isles, and is the political barrier between the two semi-autonomous regions - Mania in the highlands and Dementia in the lowlands. The difference between the two sectors is far more pronounced than whether their road signs read in miles or kilometers; their people, and indeed the landscape itself, takes the form of the area’s name.
Like Oblivion, Shivering Isles is an open world and after the first few moments you’re free to ignore the main quest and explore the islands at your leisure - but the main quest is somewhat of a “doozy.” Pop into the light at the beginning and you’ll have the not inconsiderable task of getting past the gatekeeper, that unsightly collection of body parts. We won’t spoil the solution here and now, but let’s just say that walking up to him and stabbing him in the shins is unlikely to yield much success.
Succeed, and you’ll end up in a dingy room, in which you’ll encounter Haskill, who explains that you’re now Sheogorath’s chosen mortal champion. You’ll have encountered ‘Rath before in Oblivion, perhaps - he’s the unhinged jester-type who, upon completing his quest, caused a thunderstorm of blazing bow-wows to fall upon the Khajiit clan’s land. You’ll also remember him for his Wabbajack - a mystical weapon that transforms anyone you turn it on into a random creature, for better or worse.