You think you're in a nice little Ruritania somewhere in Eastern Europe. Only the black forests are even blacker than you expected, and even more full of wolves. Some of which seem to be walking on their hind legs. When you finally get to the little town you were aiming for, the vaguely ethnic and primitive locals are huddling fearfully in the tavern, refusing to talk to you except to give vaguely-worded and heavily-accented warnings. So you go up to the castle in the hope of finding some civilization. Bad move.
If there's a local nobleman living there, he will probably welcome you warmly — although he may be strangely insistent that you "enter freely and of your own will". He will probably be the kind of old-school nobility that views peasants as farm animals on two legs. Very old nobility. Blood nobility. Alternatively, there might be somebody more modern and technically minded living there, along with his lab assistant. Unfortunately, he will probably not be big on the Precautionary Principle and make strong attempts to persuade you to "volunteer" to take part in his research. Sometimes, the castle might not even be inhabited by anybody... visible.
Congratulations. You are now in Überwald. Hope you survive — er, enjoy your visit.
Don't expect too much help from anyone: if things get really out of hand the Torches and Pitchforks might get broken out, but the locals probably think that outsiders get what they deserve, even if they aren't all actively involved in the nastiness.
Invented by Frederick Marryat (for a werewolf short story "The White Wolf of the Hartz Mountains" in The Phantom Ship; he also wrote Mr. Midshipman Easy) Bram Stoker and Mary Shelley (though Shelley's novel explicitly takes place in Ingolstadt, Germany and Switzerland), codified by the Universal Horror movies of the 1930s and 1940s, and carried on into the 1950s and 60s by Hammer Horror. Often regarded as a bit kitsch nowadays and played for laughs, to the point of being an Undead Horse Trope. Can also get you into trouble now that there are a lot more Eastern European people in the English-speaking world.
Überwald (spelled with an umlaut or as "Ueberwald" for those lacking a German keyboard), named after the Discworld country, would be a direct German translation of "Transylvania" (a.k.a. Transsylvania in some spellings), "trans silvania" being Latin for "beyond the forest". Since medieval times, Transylvania has been home to three major population groups - Romanians, Hungarians (Székely) and Germans ("Siebenbürgen Saxons"), and thus most towns and places come with a German, Hungarian and Romanian name attached. Originally, it belonged to Hungary, up until World War I, and it had a lot of German settlers. In the treaty of Trianon it was transferred to Romania (the Hungarian name of Transylvania is Erdély, coming from Erdő-elve meaning the same thing as the Latin; the Romanian is either the more traditional Ardeal or just Transilvania).
Doctor Doom's Latveria fits this trope pretty well, especially in some of the earliest comic books. It was developed slightly after Reed decides to invade although still very Überwald-ish. Everyone speaks a funny accent, there are plenty of gypsies and it seems as if most of the population are still living in thatched cottages.
Plus Doom's Supervillain Lair is a creepy castle. Although it is full of futuristic tech.
The reason Latveria is full of Romani, though, is that Doom, being one himself, is much more sympathetic to them than other nations in the region.
And the place looks old-fashioned and quaint because that's the way Doom likes it.
Marvel also has a Transylvania of its own, which is an independent nation and, unsurprisingly, an Überwald.
A Buffy the Vampire Slayer comic issue caused some offence to European fans by depicting modern Germany in this manner. It was specifically shown to be an out-of-the-way, not at all normal town, akin to a Sunnydale counterpart, but... well, Germany has a third of the US' population and is about the size of Montana. There is really no such thing as an "out of the way" place there.
Winzeldorf, Nightcrawler's hometown in the X-Men comics, is consistently depicted like this, complete with gypsy sorceresses and torch-and-pitchfork wielding mobs, despite being explicitly stated to be in present-day Bavaria.
In a similar vein, Severance is a not-too-serious slasher flick about a bunch of British corporate drones on a trip in Hungary who come across bloodthirsty psychopathic former soldiers.
The foremost advocate of the Überwald was Hammer Films. They set most of their many versions of Dracula and Frankenstein, along with several other movie horrors, in some Victorian never-never-land, not quite Germany, not quite Transylvania, not quite anywhere else between France and Russia. Hammer didn't make all this up. In the 19th Century, much of eastern Europe had German-speaking upper classes with peasants, villagers, and travelers who could be Germans, Slavs, Magyars, Turks, or Gypsies.
In Russia itself, the language of the royal court until 1812 was French. Then Napoleon invaded.
Young Frankenstein, which parodies the Universal horror movies, is another example. The film is clearly set after World War I, but the police wear Austro-Hungarian Empire-type uniforms and the whole country apparently has just one railway station! ("Pardon me boy, is this the Transylvania station?")
In Love at First Bite Dracula lived there... and ten minutes later, he was kicked out by the Romanian government.
Transylvania 6-5000 has portions of this, especially during the night scenes.
Named after a region (a collection of a lot of geo-political entities, in fact) of Discworld that is a parody of this trope, while simultaneously being a lot more true to the original than most examples. The name is a Bilingual Bonus; it's German for "above the forest", or alternatively, and possibly more true to some of its inhabitants' lifestyles, akin to Nietzsche's 'Übermensch' meaning something like 'superior forest' — in Latin, Transylvania.
Even the people there know how to handle it. Nanny Ogg gives a handy list of how to handle being in vampire country:
1. Don't go near a vampire's castle, no matter how bad the weather
2. Having gone near the castle, don't knock at the huge forbidding door.
3. Having knocked at the huge forbidding door, don't accept the invitation from the strange man in black clothes to go inside
4. Having gone inside, don't go into the guest bedroom
5. Having gone into the guest bedroom, don't—whatever you do—sleep with the window open.
6. Having slept with the window open, don't come runnin' to me to complain.
One old and particularly Genre Savvy vampire even Lampshades his own lifestyle. He lives in Dontgonearthe Castle. (With typical Tourist Trap signs posted along the road: "Just 2 miles to Dontgonearthe Castle," "Last chance to not go near the castle," etc.)
Harry Potter's Durmstrang seems to be located on one of these. The school's name is Germanic, the Headmaster is vaguely Slavic, the local superstar is a definite Bulgarian. And they won't tell you anything about the whereabouts, aside from the fact that it's very cold outside and spacious with mountains and forests. Compare with Beauxbatons and Hogwarts, which are simply French and British, respectively.
Some of Solomon Kane's adventures took place in the Black Forest, such as "Death's Black Riders," "The Rattle of Bones" and "The Castle of the Devil."
The famous British comedian Eric Morecambe wrote two novels for children, The Reluctant Vampire and The Vampire's Revenge, which are set in a parody Überwald environment.
Other children's books based around Überwald parodies include Willis Hall's The Last Vampire and Allan Rune Pettersson's Frankenstein's Aunt.
Deliberately and glaringly averted in The Historian - it's a novel featuring Dracula that deliberately tries to portray South-Eastern Europe and its culture realistically and in depth, instead of as a stereotyped evil fairyland.
The Hardy Boys Nancy Drew Mysteries of the 70s' episode "The Hardy Boys & Nancy Drew Meet Dracula" had the plucky detectives going into Transylvania for a Halloween music festival — cue the old spooky castle and villagers who still wear medieval peasant folk costumes who give the warnings about the vampire in the castle...
Principalty of Boldavia in Mystara, a province of Glantri "rumored to" be rife with undead. "Boldavia is also a large producer of garlic..." Boldavia's ruler, Prince Morphail, received his undead status as a divine "gift", turned the local nobles into vampires and/or nosferatu, and then issued the Vampire Law which prohibits his vassals from converting non-nobles and killing while feeding. Things got a bit grimmer in Boldavia, but business goes on as usual. Some of the other wizards in Glantri know what Prince Morphail is, but they realize that if someone manages to destroy him — and he's a top-ranked Glantrian — all his undead magic-using spawn will become fully free-willed at once, and no one wants to see how that may end.
More or less sums up the domain of Barovia in the Ravenloft (which also happens to be the seat of its oldest and most iconic Big Bad), although virtually all the prominent domains embody the trope at least a little. This should come as no surprise, as Ravenloft itself drew heavily upon gothic horror, both in the form of the original literature and movies such as the Hammer series.
Eberron's Karnnath used to be like this. In some places in the current era, the trope is played straight.
The titular plane in the Magic: The Gathering expansion Innistrad is home to vampires, werewolves, demons, zombies, ghosts, geists, and all sorts of nasty things. And smack-dab in the midst of this monster mash are the huddled masses of humanity, fighting an endless war against the darkness. Then, when Avacyn is freed from the Helvault...
The earlier The Dark expansion was another attempt to embody this trope.
The much-reviled Homelands expansion was also an Uberwald-flavored set. The flavor of the set (which was very good) couldn't overcome the poor quality of the set's game mechanics, and it bombed. To this day, Homelands is remembered as "that set with the excellent setting but horrible cards."
The Immortal Principalities of Ustalav in the Pathfinder setting of Golarion. This realm has Varisians (Roma) as the primary human ethnic group, a Lich (as in, The Undead) serving as its ruler for the last few centuries, and features lycanthropes, mad scientists, ghosts, and evil cults.
Sylvania in Warhammer, ruled for centuries by the Von Carstein bloodline, is considered remarkably backwards even by the standards of the Old World. It has many charming traditions, such as burying the dead face down so that if they start digging they won't be able to run (well, shamble) around the place.
It doesn't work...
The nation of Mauristatia in the Fighting Fantasy gamebook and RPG universe is like this, with vampire lords lurking in castles and mad scientists alchemists trying to build monsters out of bits of corpses.
Most of the Castlevania games take place in an Überwald setting. Some travel further afield (Bloodlines treks all over Europe, Aria of Sorrow takes place in modern Japan and/or the moon), but it's where the series' roots are.
Morytania in RuneScape, complete with all kinds of classic horror tropes: a werewolf village, swamps full of killer ghasts and leeches, haunted woods filled with vampires and claw-shaped trees that scratch at you, a literal ghost town, a Vampyre metropolis where human slaves are herded like cattle, and multiple large, foreboding, gothic-style castles. And undead chickens.
The nation of Ulm in Dominions has turned into this in the Late Age. Vampires, wolves and sinister gypsies are included. Local Illuminati add some extra color with their plots and blood magic.
The world in the first Blood Omen is a pretty straight Überwald. Less so in the following games.
Modern supernatural MMORPG The Secret World has Transylvania as one of its three main quest zones. Its 'attractions' include communist gnomes, vampires who want to take over, an alcoholic Forest God, and left-over Soviet research projects.
Rift has Gloamwood, a dark and spooky region of forest known for its giant spiders, werewolves, ghosts and walking dead, and an ancient Hag.
Quackshot has Donald Duck visiting a Transylvania that includes Dracula's Castle.
Hjaalmarch in The Elder Scrolls V: Skyrim. Features: dismal foggy swamps, a single quaint, rustic town, a large vampire lair with a scheming master vampire, an old crone with mystical fortune-telling powers as a Jarl, a strategically important fortress overrun by a cabal of bloody necromancers, no roads and a general dark, mysterious atmosphere. You can also build and own an estate there; adopted children, however, do not like to live there, they find the place too scary.
Amnesia: The Dark Descent takes place in a castle in 19th century Prussia, surrounded by black forest and the small village of Altstadt.
Girl Genius is actually set in Transylvania. Some research was done: dialogue is stated to be translated Romanian and German, one character is a Transylvanian Saxon, and another, being a descendant of a steppe warlord, is presumably a Szekler.
The upcoming Forum/RPG, Grave Academy's whole 'verse is based on this, the eponymous academy being a Haunted Castle, and the students? Monsters; although it wasn't still confirmed whether or not it is set on our world.
The Whateley Universe has Wallachia (Vlad Tepes Bessarab was Prince of Wallachia and Moldavia), which since the Iron Curtain fell has been ruled by a powerful mutant now known as Lord Paramount.
The rural parts of Litharna from The Wulf Archives tend toward this. In "All Souls' Night," Wulf visits a village whose big-city mayor wants to "modernize" the town by forbidding the old customs that the townsfolk like to practice, including the custom of leaving food for the dead on the eponymous night so that they don't rise from their graves and kill them all. True to the trope, Wulf eventually has to fight the undead, culminating in a battle with a vampire with the help of a sorceress who he's rather smitten with.
Bugs Bunny ends up at one in "Transylvania 6-5000," though he initially believes he is in Pittsburgh as a pun on Pennsylvania's name.
Spoofed in Futurama with the robot village of Thermostadt.
And more recently, planet Doohan 6, the Scottish version of the trope.
In The Simpsons, a Halloween special depicts Pennsylvania this way, with Mr. Burns taking the part of Dracula.
Out of all the states, though, Pennsylvania actually fits, outside Philadelphia and Pittsburgh. The culture is heavily Central/Eastern European, especially German and Czech, and conservative. The population is largely farmers (many of whom maintain hex signs) including the Amish, and yes, there arecastles.
In the canon episode "Sideshow Bob Roberts", the Springfield Republican Party had their meetings in a spooky castle in a place like this. (One member of the group being a vampire-like creature; the episode seemed to be one big Take That against the GOP and Conservative policies in general.)
In The Venture Bros., Baron Ünderbheit rules Ünderland, a grim and despotic land that somehow borders Michigan.
Morgana's family in Darkwing Duck lives in one, appropriately enough. The nearby villagers have access to not only Torches and Pitchforks, but also firearms, tanks, and a good sized air force.
The Fab Four visited a stereotypical Transylvania, complete with vampire, in one episode of the The Beatles cartoon (which gave us the startling revelation that George Harrison was, in fact, Transylvanian).
Inspector Gadget visited such a country (a top-secret police convention was being held there). Uniquely, he insisted throughout the episode that it was all for the tourists' benefit. There was even a haunted castle; unsurprisingly, it was Dr. Claw up to his usual hijinks.
Frankenstein's Cat is set in the village of Oddsburg, in the shadow of Frankenstein's Castle, somewhere in deepest Uberwald.