The Tanneries, Akorros

You head out through the southern gate of Akorros, and the first thing that strikes you is the smoke and steam, as if the cloud above you had come down to the ground just in that area. Peering through the fitful drizzle you see it through its grey veil, squatting on the lake shore to your right like a leprous fungal mass, filling the space between the city wall and the marsh beyond with its sheds, huts, warehouses, yards, mud, smoke and fumes.
As you head down South Road, the wind changes and the fumes roll over you, catching in your throat and making you cough and splutter with the acrid smell of urea and the overpowering stench of rotting flesh until the wind changes again. You thankfully take in breaths of the clear cold winter air again, appreciating its freshness all the more.
But your business takes you to the tanneries, so you reluctantly turn off the main road and follow a cart down the rutted side road which leads there, skins piled high on the cart still slicked with blood from the butchering. The side road is reasonably solid, crushed stone having been added to prevent the worst of the mud, and once you reach the main compound the main thoroughfares have been treated the same way, but the narrow alleys between the buildings are just thick mud, slick with an oily sheen.
Inside the wooden fence which surrounds the tanneries there is no avoiding the stench. The steam and smoke roils around and makes you cough and retch, the ammoniacal scent of urine mixing with the smell of rotting meat and the acrid wood smoke. You pass a yard full of barrels and the sharp tannic smell of the bark the skins are soaking in almost provides a welcome respite before you move past to a shed, open at the front, where workers with leather aprons and long leather gauntlets use long paddles to stir skins in large vats; the unmistakable smell of "pure" - dog faeces - make you gag.
Your guide hands you a damp scarf and you wind it around your face, the vinegar soaking it pungent enough to make your eyes water but still preferable to the scents floating on the air, and then turns off down a side street, thick with mud that sticks to your boots. You try to avoid the puddles, both yellow and red, but there is no way of avoiding the clinging mud. You now understand the strange wooden clogs he wears, raised to keep his footwear up above the worst of the mess.
Mounds of refuse by the side of the alley are live with maggots, squirming through the putrefying flesh, and flies are everywhere. A mound shifts and a pair of beady eyes look at you, unafraid, then the rat scurries off, blood damply streaking its sides.
Another turn, then another, winding around the sides and backs of the various buildings, the mud everywhere, the wooden boards of the walls stained and rotting, then you come out to another wider street. You jump back as a worker hurries past pushing a handcart laden with barrels sloshing and splashing but you are too slow to avoid the splashes of mud which spray your trousers.
Another turn takes you down another side alley out of the main flow again and you are back to wading. Now you understand why your guide said to wear your oldest boots - there is no chance these will can be made suitable for polite company again. You see a pale flash of a sheet off to your left and some ramshackle boards leaning somewhat haphazardly against the rear of a warehouse. Inside, amazingly, you see several urchins in ragged clothes and with their feet wrapped in muddy rags peering curiously round the edge at you.
This alley ends and you reach a board walk, thankfully with only a thin patina of the cloying mud; a sloshing sucking sound makes you look down and through the cracks between the boards you see water. You follow the path for a short way before the vista opens out and you can see out across the lake. Even here the foulness continues - the water is slicked with oil and blood and sucks sluggishly back and forth around the pilings supporting the board walk.
Your guide stops, pulls at a couple of boards in the wall beside you and exposes an opening just wide enough to squeeze through. Wreaths of smoke coil out as he beckons you in. "Quick" he hisses, urging you through the gap before following and pulling the boards back in place.
You eyes gradually adjust to the darkness inside, smarting from the smoke which fills the space. You move forward slowly, and your outstretched hands encounter skins hanging from the rafters, many skins packed into the space with only inches of gap between them to allow the smoke to reach every part. Your guide leads the way round the side of the building, your fingers trailing against the wooden wall on one side providing a reassuring sense of stability, your other arm up in front of your face keeping the hanging skins off. At least the ground here isn't muddy, but it's hot, claustrophobic, and hard to breathe. A skin in front of you is pulled aside and you come into a small space in the corner of the building where by the light of a small fire you see a wizened blackened figure sitting on - what else? - skins laid out round the fire on the ground. Her face splits in a surprising grin, teeth and eyes gleaming, and she holds out her hand for the purse of payment. You have arrived.

On the southern outskirts of Akorros lie the sheds of The Tanners of Akorros ; outside the city walls by decree so the noisome fumes don't offend the noses of the city populace.
Sprawling between the city walls and the marshes to the south, running inland from the lake shore, this is an area of sheds, warehouses, fences and open yards with narrow lanes running around and between them apparently at random. The ground underfoot is always muddy except even the hottest summer, with blood from the fresh skins and overflow from the tanning vats and urine baths mixing with the dirt to form an unpleasant mixture - most of the workers wear solid wooden clogs with raised cleats to keep them up out of the worst (and to protect themselves from splashes and overflows), but anyone not so shod is likely to find their footwear in need of serious cleaning when they leave (if they are lucky and the footwear can be saved at all).
There is always a great steam and stink from the various vats, mixing with the smoke from heating fires and curing kilns wreathing the buildings and rising up above in warning to the city dwellers that this is a place to avoid. It wraps around everyone venturing in, catching at throats and leaving a greasy, malodorous residue on the clothing which requires multiple vigorous washes to remove.
Main thoroughfares have been filled with crushed stone and rubble so are not too difficult to travel, but the side alleys between the buildings have rotting boards or nothing to lift the traveller out of the muck. The refuse is supposed to be collected and dumped in large pits on the outskirts of the compound, but there are many piles which have not been properly dealt with, suppurating with maggots, and covered with buzzing flies. Rats dash about freely enjoying the bounty. Open trenches down the sides of the main thoroughfares carry the effluent down to the lake where it poisons the waters and stains the pilings and the sides of the boats which tie up at them.

References:

• https://mittelzeit.blogspot.com/2017/06/leather-tanning-medieval-to-edwardian.html
• https://en.wikipedia.org/wiki/Tanning_(leather)