Ankh Morpork. A river* runs through it.
*Well, they call it a river but only because it flows slightly faster than a glacier. It’s more mud than water, the only place where the annual University boat race is held in boats with holes in the bottom and the crews run across in the surface in boots you’d only ever want to wear once.
Unseen University Archchancellor Mustrum Ridcully would rather not explain why his student nickname was “Ridcully The Brown”. Suffice to say it’s one of the reasons he prefers beer over water but no matter how many he drinks he won’t ever forget the day they capsized three times during training.
It’s a city that never sleeps.
Why would you sleep when there’s money to be earned, made, stolen, forged or recycled into beer?*
*Quite often not only all in one night but all on the same street within feet of each other.
Forget why! How could you sleep? With all the noise constantly going on? With the barkers selling their wares, Assassins inhuming, Dwarves being chucked both out of and into bars*.
*Depending on the bar, who owned it, who normally drank there and how much of a tab they still owed there.
Watchmen ringing bells at all hours telling you “All’s well!”.
All’s well! Well? The only similarity between Ankh Morpork and wellness is both seem like a deep hole in the ground with a liquid-like substance that might possibly be water* at the bottom.
*Whatever it actually is, you wouldn’t want to wash in it. Or drink it. Or use it in any shape, form or description. Even twice recycled beer is going to taste better. And get your clothes clean. Or slightly cleaner than they already were. Or at least get the sick out of them. Or perhaps at least get the smell of sick out of them.
They say if you can make it there then stay there and keep on making it and try selling it to those stupid enough to buy it because no other bugger is going to take you.*
*In other cities when they ask where you came from, the answer Ankh Morpork ususally gets the response “Too good for The Big Wahoonie? Lawks! Wot a toff! ‘Ere, ‘eave ‘alf a brick at ‘im! We don’t like your sort ‘ere. Move on**.”
**Bugger off. They might not say it, but that’s what they mean.***
***Actually, some of them WILL say it.
Because Ankh Morpork welcomed everyone.
Humans, Dwarves, Trolls, Vampires, Werewolves, Zombies and even Nobby Nobbs – not just in the name of ethnic diversity either (because no-one in Ankh Morpork knew how to spell it without moving their lips and no-one else who actually mattered really cared what it meant any way) but more by the accidental fact he was born there.
If he was born. Which many people deny vehemently. Those that know what it means, that is. Most people assume he was an accident, and not the happy kind either. The very nasty (and loudly voiced) rumour runs along the lines that his mother attracted the attention of an overly affectionate bear.
Nobby Nobbs has never denied this. He hasn’t confirmed it either. Even he isn’t sure who his mother was. Let alone his father.
In Ankh Morpork you can really get into deep trouble.
The kind of trouble that gets you dead.
The kind of trouble that gets you undead.
Or the worst kind of trouble. The kind of trouble that brings you to the attention of The Patrician.
Given the choice you’d much rather be in the kind of trouble that attracts the attention of The City Watch. At least with Sir Samuel Vimes you’d get a fair chance and a lot of sarcasm. If you were injured they’d treat your wounds, maybe. Or let Igor see them. And maybe laugh at them. Or take iconographs of them if he thinks they are particularly interesting.
He’s that kind of Igor.*
*They all are. Ignore any Igor who says he isn’t. Igorinas may be different.**
**It’s highly unlikely they are but it’s possible. This is the Disc, anything’s possible.***
***See footnote  below.
It all depended on how you got them. There is even the chance of a lawyer as long as you don’t call Mr Slant, Vimes hates him.
Don’t let yourself think that the City Watch had the market cornered on matters relating to criminal investigation. Far from it. Well, not quite far. There was one other avenue open to those in desperate need and you’d have to be pretty desperate to procure the services of Lewton, Investigator for hire and occasional loan.
When those under the scrutiny of the law say “There’s no justice”, Sir Samuel Vimes is quick to point out “There’s just us.”
Lewton eventually points out “Hey, there’s me as well!“.
Fortunately The Patrician has no need to point out there’s also him too.
Everyone is more than aware he is there, many wish he wasn’t. But the kind of justice he dispenses is normally in coiled hemp form, through a trapdoor. There’s also the door he offers you the free chance to walk out of. It’s very suspicious. Everyone knows about it, no-one knows anyone who’s ever chosen it.*
*Chosen it and lived to report on the matter, that is.
Lewton doesn’t investigate very often, it’s more a hobby. Well, not really a hobby. More a good way to pay his rent and buy important things like food. And the continued attachment of his legs to the rest of his body. 
 Continued attachment to your legs is not always possible in Ankh Morpork. Especially after hearing phrases such as “Mister Chrysoprase is very upset with you.”
Lewton likes his legs. He likes them attached to his body as it allows him to walk around the city to investigate.
They say all roads lead to Ankh Morpork.*
*Those that don’t fair well and need to make a hasty escape also know all roads lead away from Ankh Morpork to a myriad of places where you aren’t going to asked questions like “Was it you that done it?”
And all walks of life travel on those roads. Some by coach, some by horse and the rest have to walk. That’s probably why they’re referred to as walks of life. It may not take a lifetime to reach your destination but on certain roads it’ll feel like it.