Location: southwest of Weatherleah, which is south-southwest of Chorrol (link goes to the Daedric Shrines map at the UESP Wiki)
Minimum Level: 8
Offering: Cyrodiilic Brandy
Reward: Sanguine Rose
Objective: liven up a dinner party for the Countess of Leyawiin
Finding the shrine isn't terribly difficult. Three people can mark it for you, the easiest to find is Falanu Hlaalu at "All Things Alchemical" in Skingrad. Just follow up on the "Daedric Shrines" topic. The offering of Cyrodiilic Brandy may be the first sticking point. Although it does turn up as leveled loot occasionally, you'll probably need to go hunt one down. There are a lot of them out there, but you'll probably have to steal it. A few innkeepers might have it, but you might have better luck with Alchemists, including Ms. Hlaalu (hers is iffy, but she has it occasionally) and at "The Main Ingredient" in the Imperial City (where it should be a staple).
Once you have the brandy, go to the shrine and activate it. Sanguine wants you to liven up what promises to be an otherwise "stuffy" dinner party with a special "Stark Reality" spell. So hop on down to Leyawiin and crash the party. There's a guard blocking the doorway to the dining room, but if you're dressed nicely or you raise his Disposition to 70 or more, he'll let you in after 6 p.m. Once everyone is assembled, cast the spell. The Countess and her guests start running around in their underwear (or are "Stark" naked, if you've installed that mod). Mission accomplished, sort of. You see, you're in the area of effect for the spell (maybe Sanguine thinks you're too stuffy, too), and the guards aren't too happy with you at the moment. You should probably beat feet for the door and pray that you don't get stopped. You don't have any gold to pay the fine, so it's either go to jail or resist arrest; the first being bad for your skills and the second being bad for your health. Resisting arrest can be done, but it will take a while to outrun the guards so that you can fast-travel again. If necessary, you can clear up the fines after you get your stuff back.
Once you can, fast-travel back to the shrine. Sanguine rewards you with the Sanguine Rose (it summons Daedra) and points you to a now-unlocked chest where you can get your stuff back.
Although I don't generally keep track of fan mods, there is one out there that lets you buy the "Stark Reality" spell from Edgar's Discount Spells in the Imperial City.