I could tell you how I represented Darkspine, a city in the first layer, in one of my adventures. The baatezu tricked the ruler into letting his town enter Baator. He is still technically governing it, but he's got nothing to rule over, and the devils wait for him to die to drag his screaming soul into the last of the larvae. The town is almost completely in ruins, and a large portion of it is burning. The PCs were forced to obtain faked documents to enter, and they occasionally have to show them to an abishai patrol - and every time, they might be caught. The ground is full of debris and jagged rocks, and the PCs can't run (if they try, they have to make Balance checks or take damage). Some of the stones bear an eerie resemblance to humanoid faces. The sky is reddish, and the air is cold.
But more than the landscape, it was the encounters that made sure the PCs wanted to get out of there as soon as possible.
- A gelugon and a night hag are bartering for a herd of larvae the hag is guiding. The larvae all have ghastly and distorted human faces. The hag offers one to the fiend, saying how fresh they are, and the devil tears a leg off the creature and eats it as the larva screeches and cries. The hag says "I'll give you all of them for the amulet and if you add a nice spellbook...", to which the fiend replies by throwing the wounded larva far away (it splatters near the PCs' feet). "Ok", says the hag, "The best fifty of them for the amulet alone". The devil agrees and finds one of them is crawling up its leg. The gelugon's tail whips and the larva falls to the ground, broken but still twitching. The fiend picks it up and slowly crushes it, letting the blood spill to the ground, until the screeching stops.
- As an abishai passes near, followed by two lemures, one of the lemures wanders away and attacks one of the PCs. The abishai immediately orders it to stop and come back - then, with not a word and a fast slash of claws, tears the lemure apart and proceeds on its way.
- A sphere of flames blobs out of the ground near one of the city's derelict inhabitants. As he turns to run away, the globe explodes, and when the afterlight fades the PCs can see the man wrapped in flames run screaming for a few moments before dying.
- On the ground, near a wall, an old man clothed with rags sits and keeps repeating the same sentence "I'm loyal to Bel, I'm loyal to Bel, I'm loyal to Bel", over and over again. On his exposed shoulder, the PCs can see a mark; the skin is burned and covered in bleeding plagues. No matter what they say, the man won't stop saying the phrase.
- The PCs pass near a man who has managed to capture a larva and is happily roasting it over a campfire. When they are going away, they hear a quick scream behind them, and turn to see the man dead with his throat slit, and someone running away with the cooked larva.
- The PCs are attacked by a group of derelict Darkspine inhabitants. They have just knives and rags, but they fight to the death. It's not like they'd lose anything, after all.
- While the PCs are inside a building, a team of four abishai barges in dragging a woman, kicking and screaming. They turn to the PCs and one of them says: "Out of here. This woman has decided to swear fealty to archduke Bel, and for the oath we're going to need some intimacy". Meanwhile another abishai is holding a branding iron, which is quickly becoming red-hot in the fiend's fiert grasp. Moments after the PCs are out, they can hear female screams from inside.
...and on, and on, and on. And this is only the first layer, and one of the most hospitable places on it, too.
