Remedial Ravenloft: Dementlieu

Before - Throw some French at the wall and see what sticks.

After - A three-way courtly battle between Fantomas, the Phantom and a psychic hellfire club backed by the Deep Ones.  That is to say, the French that stuck.

Where is it - A city state on one of the nicer stretches of coastline.  Western Core, on the Sea of Sorrows.

Technical Advancement - Analogous to western Europe, mid-late 18th Century CE.
Supernatural Advancement - Supernatural powers are common amongs the upper classes, tutelage and artifacts are available for purchase, some supernatural public works.  Powers focus on psychic/mental development and contact with alien entities, mostly ones located in the barrier reefs beyond the bay.

The Land - The city of Dementlieu is grand and old, old and grand, spires, steeples, towers; they say that Dementlieu and Richemulot built their cities as high as one another, just that Dementlieu started at ground level and Richemulot started a lot lower.  There's not much of an underground in the city, being very close to the water in both proximity and elevation.  Canals are a major method of transportation in the city, and, yes, a visitor from our world would be forgiven if they thought someone mashed Paris and Venice together, with regard only for brooding, picturesque atmosphere.  Sometimes the obvious choice is the correct one.  The city is in a surprisingly well sheltered and defended harbor, covered by state of the art guns and star-forts, and is the major hub of maritime trade.  Ships from all over the Core and the Sea of Sorrows are constantly coming in and out.  Countryside is actually really nice, coastline rising pretty quickly into rocky, lightly forested hills.  Dementlieu controls a number of barrier islands out in the Sea of Sorrows, many of these are reserved by the Council of Brilliance for official use, and range from manicured manors to creepy, stinking tangles rising from the sea.

The People - Dementlieu is the cultural center of the Core, so when the Dementlieuese say that (and they will), they actually have something there to back it up.  Dementlieuese fashion, music, art, education and thought are in high demand just about everywhere they have a little money to spend.  Artists and poets and fashionistas all over the Realm learn Corbeau so they can grab some of the glamour.  Dementlieu is one of the few places in the Core with a strong (and comparatively affluent) middle class and some... well, we'll give them the credit of having progressive ideas and ideals in government.  In practice, there's a huge and impoverished underclass that's just as ground down and kicked around as any vampire-bitten Barovian serf, but there's public education, so of course that's not really the case.  Dementlieuese overall are, again, fairly diverse, owing to their status as a maritime hub, but the upper classes lean toward light skin, dark hair and eyes, speak Corbeau and tithe at the Dementlieuse church, though religious conviction is something for the poor.  Most Dementlieuese are superstitious about the islands and reefs beyond the bay, and new moons are the nights where everything locks down in the city and surrounding countryside, opposite basically the rest of the Core.  Mists tend to freak them out as well, though that's fairly reasonable.  Dementlieu gets more frequent and heavy visitations from the Mists than most Domains seem to, and those either bring more active Mistbound predators or encourage local predators to come out and play.
Wag's Eye View - Posh douchebags.  Even the desperately poor in Dementlieu manage to be desperately poor posh douchebags, somehow.

The Boring Stuff - Less boring, owing to the viciousness that goes on below the surface.  The city-state of Dementlieu is technically a republic run by an elected council called the Council of Brilliance.  In theory, election is popular and open and anyone with sufficient votes could win a seat.  In practice it's about as open as a totally unsupervised high school club's office elections, and to the extent that it is a popularity contest, it is popular.  The names of those up for election are determined in social clubs for the ultra rich that meet behind closed doors and practice dark arts.  No shit, actual Dark Fucking Arts, because that's the kind of jaded we're dealing with in Dementlieu.  Hellfire clubs used to be common passtimes for the elite, but they have since grown into a sort of shadow establishment to the official government.  Each one has a different specialty, as those things go.  Weirdly, though, the city has seemed to benefit from both the high level of supernatural power the aristocrats often develop and the canceling effect of multiple alien entities with interests in owning the city outright.

AND I WANT AND I WANT AND I WILL ALWAYS BE HUNGRY - And there's the rub.  The secrecy and supposed depravity of the hellfire clubs makes it near impossible to figure out how Dementlieu came to be a Domain or who might be it's Darklord.  There's just too much to choose from and most of the choices are well hidden from even the local crusading detective (Alanik Ray, member of an especially long-lived near human species and a righteous pain in the ass of almost everyone, but too useful and canny to just kill off.  So Far), making it very difficult to pinpoint who, when and how it happened.  We know that Dementlieu was very successful for a very long time, and prosperity led to boredom among the upper classes, which led to interest in developing supernatural powers, a practice which may have actually been forbidden by their religious establishment (the secrecy seems a little extreme given that Ezraism, while ambivalent, does not forbid development of man's natural capacity to contend with the supernatural, and the Dementlieuese church is one of the more liberal branches where that is concerned).  This created the culture of the hellfire clubs, and we're pretty sure some posh asshole brought Dementlieu into the Mists to impress his douchey friends.  Fucked if we know which douche and when.  We're prone to taking it on faith that Dementlieu and Richemulot were born into the Realm at the same time, but Richemulot's history is no help in that matter, either.  They might have been the same Domain initially, or conjoined like Borca and Dorvinia.  They might have been a buy one get one deal for the Dark Powers (any Dementlieuese hearing that would be quick to call Richemulot the one the Dark Powers got gratis).

The Darklord Could Be... It could be Dominic D'Honaire, current (and long-running) chief executor of the Council of Brilliance.  An apparently unassuming man who is, nevertheless frighteningly popular and, if we're being honest, a damned good chief executive as they go.  The irony is that he gets to be on this list based on what we do not know about him.  His public persona is that of the public servant, unpreposessing and unflappable, cajoling order and progress out of the nest of vipers that is the rest of the council.  The fact that he's been doing this with incredible success, considering, for four consecutive five year terms without telekinetically impaling someone on the spire of the Grand Cathedral (it's happened more than once; actually, it was first done by Dominic's father during his term on the Council.  Man was a trend setter) is telling.  You don't get to survive in the big chair, let alone succeed unless you're the devil.  Also, motherfucker hasn't aged.  That's a dead giveaway (really, it's not, a half dozen of the other members of the Council are suspiciously well preserved; one might be breaking in a full body transplant courtesy of his contacts in Lamordia).

...It could be the Brain, criminal mastermind, probably a powerful telepath, weaver of memories and perceptions who has been plaguing the Council and everyone else with high profile, occasionally brutal crimes for slightly less time than his proclaimed nemesis D'Honaire has been running the council (the fact that the Brain calls D'Honaire "nemesis" lends creedence to the notion that it's him, I swear).  It's Dementlieu and the Brain is still operating, so it's clear he's damned good at keeping his secrets.  The only thing we know of the man for certain is the crimes for which he has claimed responsibility.

...It could be the lonely figure that prowls the quayside theater district, disrupting productions, seducing young stars, causing scandal, murder and mayhem and is linked with a rival master criminal, less established than the brain and more theatrical (see what I did there) who goes by "The Phantom."  Or the lonely figure that prowls the Grand Cathedral, scaring the be(crystal dragon)jeezus out of novices and acolytes, blending in with the gargoyles and ringing the bells at odd hours.  Or the lonely figure sometimes seen swimming in the canals (this is a super bad idea), or out on the wharfs on moonless nights singing weird songs to the sea.  Fuck Dementlieu.  Seriously.  Well, the food is nice.

Land of Opportunity - Seriously, if you cannot find something profitable, shady and violent to do with your time in a city state run by secretive magicians and psychics who have more money than they have venom for one another (and only because they have truly ridiculous wealth), where theatrical master criminals engage in battles of wits with (let's be honset, Alanik), theatrical master detectives, I don't even know what I could do to help you.  Just write everything down - your memories of your time in the city might not be accurate, and not just because of the wine.

Closing the Borders - Closed borders just shroud the city state in Mists, and each bank of fog is a Mistway to wherever in the Domain the Darklord wants to see you end up.  It's efficient, understated (LIKE D'HONAIRE).