Location: South of the Silverfish River, a bit east of the Imperial Bridge Inn (link goes to the Daedric Shrines Map at UESP Wiki)
Minimum Level: 10
Objective: release Peryite's worshipers
No one tells you about this shrine and it's not likely that you'll stumble across it on your own unless you're hunting Nirnroots. If you're hunting Nirnroots, it's pretty likely that you'll find it with no problem since you'll be following the Silverfish River and the shrine will show on your compass. It's on the southeast bank of the river, a little way east of the Imperial Bridge Inn.
When you get to the shrine, you'll find the worshipers just standing around in a circle. If you try to activate any of them you'll get a message telling you that they are unconscious. If you're level 10 or higher, you'll be able to activate the shrine. Peryite will tell you that his worshippers' bodies are here in the moral realm while their souls have been sent to Oblivion. You'll need to go there to retrieve them. If you've been closing Oblivion Gates, you've got a good idea of what to expect. If not, you can expect leveled Daedra - a lot of them. Aside from Boethia's quest, this is the only other Daedric quest where you have to go to Oblivion. And, aside from Nocturnal's quest, it's the only one that requires no offerring (could be because there's no one who can tell you what kind of offerring to bring).
When you arrive in Oblivion, you'll need to find the five worshippers' souls. They're really kind of scattered around the map, but they have individual markers, so they aren't terribly difficult to find. But because it's Oblivion, the route is not terribly direct. As you get to each soul, activate it. When you activate the last one, return to your starting portal to get back to the shrine. The worshippers don't seem too thrilled to be back among the living again, but Peryite seems relatively happy about it. He/It gives you Spellbreaker, a shield with a pretty decent Reflect Spell effect.