Skyrim Sidelines- The House of Horrors: The Old Man and the Stone Door

As you pass through Markath, you may note that there is a building you simply can't enter, built into the North wall of the stone city.  Your second time in the city (and any number of subsequent times) you'll run across a cowled man outside the front door of the home.  He may be talking to a Nord by the name of Yngvar, inquiring if the man has observed any strange lights or sounds coming from the abandoned home.  Yngvar says he hasn't, and the priest, Vigilant Tyranus, turns to ask you the same.

Answer as you like- the priest will still explain.  The hooded man says that he is a Vigilant of Stendarr, an order dedicated to the destruction of anything related to the Daedric Princes and Daedra worship in general.  He may ask for your help, or you may offer it to him- you can, of course, refuse to do so, and he will simply show up again some other time in the same place, for the same conversation.

Eventually you'll likely get tired of this and agree to help the guy just so you can wander Markath unmolested.  He will enter the house, and tell you to follow him in.

As you enter, the building will appear to be completely fresh and lived in- there are no cobwebs, the furniture is in good condition, and there's fresh food sitting about, waiting to be cooked.  You can wander around briefly, as will Tyranus- and then a basket rolls across the floor.  A faint moan sounds, followed by a ground-shivering rumble, and Tyranus takes these signs to mean that something here is wrong.

The Vigilant will move further into the house, opening a door to look through as the building fills quickly with a faint fog.  Tyranus will head down the stairs found on the other side of the door and begin looking around, shouting for the being here- who and whatever it may be- to show itself.  You will have a few moments to explore as well, before a voice prompts you to open another door- whichever door you choose, it will prove to be sealed and unopenable.