A Visit to the Fiddle
In the city of Lundeinjon, on some street near Eastbridge (the exact location varies), you find a nondescript door with a shattered fiddle nailed to the wall above it. The door is always closed - and always unlocked. The handle is sticky and damp, and the door makes a wet squelch when you open it.
Inside, the room is small and dark. A single gas lamp burns on the wall opposite the door, its light dim behind a sheen of soot. Everything in the room is moist and warm, and strangely yielding to the touch. The floor is tacky with something that might be old beer - or might be something more… organic.
A half-dozen tables stand about the room, all empty. There are never any customers here. The chairs are slightly askew - look closely, and you'll see that the legs are sinking a little into the floorboards, which are softer and more pliant than wood has any right to be.
To your right is a bar. It's upholstered in pale leather, scuffed and stained, and the counter above it has the cracked, yellowed look of ancient ivory. There are no stools.
Behind the bar stands a tall, man-shaped figure. It's pale and enormous, and doesn't seem alive until its eyes swivel to fix on you. If you order a drink, the creature serves you. If you drink it - well. There are more foolish choices in the world than swallowing the noxious ale of the Fiddle, but not many.
People don't come here for the drinks. They come to speak with Mr. Rat.
Beneath the bartender is a small, puckered hole. You ask to see Mr. Rat, and the pale figure nods and waves you behind the bar. As you approach, the hole dilates open. It looks dark, wet, and gently quivering. You were warned about this beforehand, but it's worse in person. Still, you step into the hole, and it clenches around you, pulling you down below the floor.
The journey to Mr. Rat's lair is swift and horrifying. The walls of the tunnel pulse and twitch, slick with some foul, mucilaginous paste. Then, without warning, you drop out the bottom and land in a steaming heap of something you refuse to identify. You rise slowly and look around.
The chamber is round and dim. A single spark of light hangs in the air above the center, glowing a dull orange-red. Beneath it sits a small man in a faded suit, a bowler hat perched on his head. He grins as you approach, teeth too sharp and too many. When he rises to greet you, the muck slides off him without leaving a mark.
Your business with Mr. Rat is not to be spoken of. He deals in secrets - things glimpsed within the city's bowels, or overheard in the dark and hidden places. Perhaps you are offering one. Perhaps you are buying. It doesn't matter. He never stops smiling, and after a time you stop noticing the smell.
The moment you realize you no longer smell the place, you know you've been there too long. You conclude your business and turn to leave. Mr. Rat smiles wider and gestures upward. The fleshy tube that brought you down extrudes again, wrapping around you and dragging you back up, ejecting you into the bar above.
You should be gagging - but you aren't. Your capacity for disgust has been dulled, smothered under something vast and numbing. You pull yourself upright and stumble for the door. You no longer care what you touch. The wet, vile room seems almost familiar now.
You step back into the night, leaving damp footprints along the cobblestones. You don't think you'll ever be clean again. When you pass a ditch, you stop and rinse your hands in the water there. Someone has used it as a latrine - but that doesn't matter. It helps anyway.
What does clean even mean, after all?
A Vile Inn
The Fiddle, and its attendant figure known as Mr. Rat, are associated with the eldritch entity called The Broken Bowel, and are said to operate in many cities across the world. The doorway to the Fiddle moves unpredictably, but it is always marked by a shattered fiddle nailed to the wall nearby.
Mr. Rat is reputed to traffic in secrets and lies - sometimes taking visible pleasure when someone lies to him, and often requesting more. For reasons unknown, his excited whisper of "Lie to me" is rarely appreciated; some people claim that hearing it once ensures a person will never again speak a falsehood in his presence.
When the Fiddle appears, it is often accompanied by outbreaks of disease and waves of crime, particularly those involving gore, excrement, or filth. Rats and other vermin multiply in its vicinity, and sanitation systems frequently malfunction - pipes invert their flow, sewers overflow upward, and decay spreads through once-clean streets.
Those who enter the Fiddle report intense disgust that fades with exposure, leaving them strangely indifferent to foulness thereafter. In time, they are said to be offered the chance to stay in one of the Fiddle's rooms. None who accept are ever seen again.

Well that was "disgusting" in the most amazing way possible. You really nailed this prompt. This place is macabre and so vividly detailed that I could almost smell it. The second person narrative elevated even more! I am so very curious for Mr Rat and I hope they get their own article at some point :)
Thanks! This was actually originally an ad-hoc encounter in the first game I ran in High Albion years ago...one of my players walked past all the red flags and wound up making a deal with Mr. Rat. As you might imagine, it hasn't gone as well as he might have hoped. :)