The City
The setting for Eyes in the Dark is "The City" -- a fictitious city somewhere north of Chicago, always referred to in-game in the non-specific.  Rather than an party-mission-adventure based game as is standard to RPGs, Eyes in the Dark works instead on a single geographic boundary in which the players can freely engage in whatever activities they want, lending itself much more to political, subplot-type stories than standard hack-n-slash adventuring.  It also allows the player group to consist of many different characters, all shades of gray.   Whereas inter-player conflict can ruin a standard RPG, it is the backbone of I2D.  Is this monster my ally in this, or my enemy?
 The City itself is, on the surface at least, a very ordinary modern city with its urban sprawl, suburbs, police, homeless, bars clubs, and so on.   However, this skin of normality conceals a terrible secret: That monsters exist and thrive in the city.  Outwardly, the city is prosperous, successful, boasting one of the lowest crime rates and unemployment in the country, and the least number of homeless anywhere.  The reason why is both grisly, and obvious.  The people do not, or pretend that they do not, know that the monsters are there.  Nobody is entirely sure why, least of all the fiends themselves, but they aren't likely to challenge it too strictly.
Many of the city's fiendish dwellers maintain at least the illusion of humanity.  They own stores or businesses which front their lairs and allow them the comfortable living of civilization, even if their own undead lives are marred with violence and horror.  The best known of all these fronts is NightStalkers, a club downtown where all the monsters can go to meet and mingle with their own kind, under the watchful eye of the Master, the self-proclaimed king of the  The City: An ancient and terrible monster with, nevertheless, a wry sense of humor.  The top levels of NightStalkers are open to the public, but the secret sub-basements are for monsters alone, all mortals to be killed instantly if they broach that frontier.
The other major figurehead of The City is not a monster at all, but a man.  A greek magnate called Stavros, who assists and befriends monsters.  Though he seems sincere and has the trust of many of the mutants, the fact that his XTRA Labs conduct research on monsters, and that his weapons companies supply anti-monster groups like The Red Moon makes him appear more than a little suspicious.  He will do anything to help a monster in need, yet he created and funds the secret monster police, XTRANS, who will disintegrate any monster who murders masses of people.  Is he friend or foe?
Many of the reems of not-so well-to-do monsters live in the Haunted Quarter, a large section of the city which is run-down and mostly forgotten.   It is also home to many homeless people, which makes an attractive territory for many a monster-- camouflage and a fresh supply of food.   Another happy circumstance is that a large earthquake buried part of the city in the 1800s and now large sections of ruins lay deep in the underground, another convenient lair known as the Sunken City.
For one reason or other, very few people of note come from The City.  It's a subject of some of nervous giggles that most people who grow up or live in The City any length of time usually wind up on drugs, taking pills, or in therapy.   Nobody admits they know why.  One who did, however,  is Bain the Sidhe, a rock singer whose gritty dark style depicting the horrors of modern society has recently come into popularity.
Read more about the mythology and history of Eyes in the Dark.