The Dark World segments of Dungeon Keeper Ami have a certain vibe that reads like this. Actually played with to some extent- the waylaying, slavery, debauchery, and general amorality aluded to is pretty typical and even expected of the underworlders. Further enforced by the various cults of the Dark Gods. Some of the cities are actually fairly clean, leading to Vice City feel.
Apple Bloom: This is my kinda town. Dark, crowded, full of ponies that aren't you two nut jobs.
In the Winningverse, and particularly in The Freeport Venture, there is Freeport, a Not-So-Safe Harbor run by a cabal of greedy merchant-princes, with guards so corrupt they are expected to supplement their income with bribes, and a haven for mercenaries, spies, and legalized piracy. Since it sits on an archipelago right between Equestria, Gryphonia, and Zebrica, none of those nations can make any move on it without the other two seeing it as a threat, which is what allows it to remain a Wretched Hive.
In Gensokyo 20XXV, we have "The Forbiddens", which are considered to be a no man's land, and, compared to the rest of the setting, these are the worst places to be, especially if one be woman or child.
Amoridere: The Forbiddens is where the worst of the crap that tends to occur in this society occurs. Women and, sometimes, children are sold into prostitution where they tend to die and children are traded for just about anything or killed just because, as well as the fact that most of those areas are laced with various traps, the which of include landmines, snares, bear-traps, and vicious dogs, on top of the fact that those areas are best know for their pollution and toxins, as well as its corrupting influences.
Pokémon Reset Bloodlines portrays the Orre region this way. It's a barren wasteland where only the strong survive, and Cipher pretty much controls it. Agate Village is one of the few safe havens where they don't have any influence.
Season 2 of The New Adventures of Invader Zim introduces the planet Slumia. Due to being of little importance to the Irken Empire's military-industrial complex, instead being mostly used as a dumping ground for the civilian population, it is overcrowded and underfunded, being left with crumbling infrastructure and a powerful criminal element. In fact, it's established that outside of the small portions of the planet under direct military control, it's controlled almost entirely by the Green Claw Syndicate.