Old Dark House

You know that old, foreboding house up on the top of the hill, surrounded by thick forests, and accessible only by a single bridge that has a tendency to wash out during every rainstorm? Yeah, that one. Have you ever noticed that it always seems to attract eclectic groups of strangers who get invited for the reading of a will or a dinner party with a mysterious host? And why is it that the strangers keep getting killed off, one by one, during the night? It must be one of them doing it? But which?

Expect many passageways hidden behind bookcases, usually operated by candlesticks, portraits with removable eyes for spying, and the ubiquitous thunder and lightning. Almost inevitably all methods of communication with the outside world—especially telephones—will have somehow ceased to function, if they ever existed at all. This was more plausible in the early 20th century, a.k.a. Agatha Christie Time, when many old dwellings had not yet been fitted with telephones and service in general was commonly more apt to fail. You can also expect the lights to go out several times during the night. (Usually when it's least convenient.)

May or may not be haunted or have some curse or be hiding a Dark Secret. If the mystery is set in Europe, this may be a castle instead of a mansion. See also Haunted House, Haunted Castle which usually are haunted. In this trope, while a haunting may be real, it is more likely that the mysterious poltergeist is an elaborate hoax.

Please keep in mind that not any old house with poor lighting will do for this trope. This is a classic trope of, and a great set piece for, whodunnit murder mysteries.

Examples of Old Dark House include:

Anime and Manga

The ×××HOLiC movie A Midsummer's Night Dream takes place in one of these. Though the house itself is the one making the guests disappear.
Umineko no Naku Koro ni: The Rokenjima mansion, complete with being cut off from the rest of the world and its own witch stories.

Board Games

The board game Clue (aka Cluedo) is perhaps the best known example of this trope.
The game Kill Doctor Lucky, which is inspired by Clue, also takes place in such a mansion.
Betrayal at House on the Hill takes place in one of these. Though you usually know who the bad guy is.
13 Dead End Drive is a board game with this as the set piece and the players as potential heirs trying to bump each other off.

Comic Books

The titular House of Mystery and House of Secrets horror anthologies from DC Comics, which later featured in The Sandman.

Film

Clue the movie took place inside such a mansion.
The 1932 movie The Old Dark House (as well as the 1963 remake) is the Trope Namer.
- Both movies are based on an old novel, Benighted, by J.B. Priestly.
Larry Blamire's Dark and Stormy Night is an intentional Affectionate Parody of this genre with a couple of Lampshade Hanging moments.
An old Bela Lugosi movie called Ghost Story took place in such a mansion. Though since the movie was primarily meant to be humorous, there was no murder involved.
The Don Knotts film The Private Eyes featured one of these where the house staff are being knocked off one by one some time after the the lord and lady are murdered.
Murder By Death is one of these movies, only the guests are all pastiches of famous fictional detectives.
Even though it takes place in a radio station during a live show, The Radioland Murders plays this trope pretty well. The biggest difference is that only certain important people conected to the station are in danger, and not everyone in the building.
The original House on Haunted Hill certainly takes place in one. The remake is more of a traditional Haunted House.

Literature

Agatha Christie's And Then There Were None took place on a mansion on an island, and the boat wasn't coming back for several days.
Sarah Waters' The Little Stranger takes place in a decrepit, isolated old manor house in Warwickshire.

Live Action TV

The Adventures of Brisco County Jr. had an episode that took place on an island during a gathering of famous bounty hunters where someone begins killing them off.

Theatre

The Cat and the Canary, where a young heiress and her relatives are harassed by a killer.
The Bat is set at the house of Courtleigh Fleming, the late president of the failed Union Bank. Rumor has it that the money robbed from the bank is stashed in a Hidden Room in the house. In an old country house whose lights tend to fail during storms, candles, pocket flashlights, and wristwatches with illuminated dials all become important items.
Parodied by the play-within-a-play in Tom Stoppard's The Real Inspector Hound.

Video Games

5 Days a Stranger takes place in one of these.
One of the Dark Brotherhood mission from Elder Scrolls 4: Oblivion sends you to one of these, only you are the murderer. (Though it's possible to convince the guests to kill each other.)
Lucius plays this trope much like the Dark Brotherhood mission from Oblivion. You play a child of the devil who must kill everyone else in the house without arousing suspicion.
The Verlac mansion, in the titular town of Anchorhead, has hidden passageways, unsettling paintings, windows painted shut, and a Madman in the Attic.

Western Animation

This is a staple of Scooby Doo and many of its imitators.
Wayne Manor comes across as this in the pilot of Batman Beyond. The secret that it is hiding is a little unconventional, of course.