As depicted in Tim Burton's 2012 film adaptation of Dark Shadows, Collinwood is the New World family mansion where the Collins family from England settles in about 1760 and maintains its home until (at least) the film's concluding events in late 1972.
Built showily upon a promontory high above the Maine fishing village of Collinsport, both the mansion and the town are named for their founders, Joshua Collins, his wife Naomi Collins, and their young son Barnabas Collins, who - as an adult - is the film's principal protagonist and who narrates some of the story of Collinwood's construction. The mansion is shown to be situated a short distance away from a precipitous cliff called Widow's Hill, which overlooks sharp, wave-battered crags washed by the Atlantic below.
According to one of the mansion's principal heirs in 1972, Elizabeth Collins Stoddard, the mansion contains over 200 rooms, but most of the house has been sealed off to reduce energy costs as the family's fortunes have declined. Among the rooms still in use that are shown in the film, there is a large foyer with a double-doored entryway from the outside, featuring elaborate stone and wood carvings of mostly aquatic themes, a collection of elaborate framed painted portraits, and a prominent chandelier featuring elements resembling the tentacles of an octopus; a dining room with damaged but impressively sized sea-themed painted murals; an improvised in-home laboratory and psychiatric office; a cylindrical tower room adapted as a shag-carpeted and poster-papered bedroom for Elizabeth's 15-year-old daughter Carolyn; a coatroom; and a small bedroom used for the household's hired governess. Among the more impressive rooms is a large drawing room with a writing desk, electric organ, grand piano, chaise longue, and hidden access points to at least three secret chambers, one of which is pivotal to advancement of the story.
At the time of Collinwood's two new arrivals in the film, the live-in governess Victoria Winters and the 200+ year old vampire Barnabas Collins, the house is occupied by the only four modern heirs to the Collins estate, Elizabeth, her 15-year-old daughter Carolyn, Elizabeth's brother Roger and Roger's young son David. Three Collins family employees also reside at the mansion: the live-in psychiatrist Dr. Julia Hoffman, who has been at Collinwood for three years; and the long-time maintenance staff consisting of caretaker-handyman-chauffeur Willie Loomis, and elderly housekeeper Mrs. Johnson.
(Unlike in the classic television series, there is no mention of an "Old House" on the Collins estate, and the implication is that Collinwood is the original family residence, though of course they would have had to reside somewhere temporarily during the construction phase depicted in the film.)
[If you have not yet seen the film, plot details below may contain spoilers.]
Though the source of their original wealth is not stated specifically, the Collinses clearly arrive in the New World with ample Old World economic resources to launch an initially prosperous fishing business and to build the elaborate Collinwood mansion from scratch using the work of fine Old World craftsmen and extravagant imported materials. Fatefully, they also arrive with servants, among them a woman, apparently of Continental and possibly French origin, named Bouchard, and her dark-haired young daughter, Angelique, who will develop into the family's (and the film's) great nemesis.
After reaching adulthood, Angelique's class resentments, combined with her spurned love for Barnabas, his new relationship with Josette duPres, and Angelique's talent as a student of witchcraft, cause her to cast a spell in which a large chunk of the Collinwood mansion's decorative maritime-based masonry - a seahorse statue near the roofline - becomes dislodged from its perch and plunges down upon Joshua and Naomi, simultaneously killing Collinwood's original owners. This occurs in or around 1776, and is followed by events leading Angelique to impose the vampiric curse upon Barnabas, bury him "undead" in a chained coffin, and plot the economic decline of the Collins fishing business while enriching herself.
196 years later, in 1972, a twist of fate enables Barnabas to escape his coffin confinement and return to Collinwood, which by this time has greatly decined from its glory days. Barnabas then reveals to Elizabeth the most elaborate of the secret rooms his father had had his architects design beneath Collinwood. The huge fireplace in the drawing room, when "unlocked" by a knowledegeable opener such as Barnabas, proves to be a lever-actuated portal, receding back (with mechanized howling decorative wolves, no less) to display a large opening into a dark subterranean hollow beneath the main floor. Barnabas leads an initially wary Elizabeth down a hidden stone staircase, along a rat-infested secret hallway, and into a long-unvisited vault housing a treasure trove of artifacts and centuries-old wealth. "We've been sitting on a fortune!" Elizabeth marvels.
Barnabas uses the newly unearthed wealth to renovate Collinwood, which - due to the family' s relative impoverishment through Angelique's continued machinations - had fallen into considerable ruin between its opulent construction and Barnabas' return in 1972. A large party (a "happening" or a ball, according to Carolyn and Barnabas respectively) is given to celebrate Collinwood's refurbishment and many of the townspeople - not including Angelique - are invited to attend.
Angelique crashes the party, is further infuriated to find Barnabas romantically involved with Victoria Winters, and plots further to destroy the two lovers and the Collinses. She eventually returns to Collinwood and uses magical powers to turn the mansion itself into a weapon against its owners and inhabitants. (This, of course, echoes the way in which Angelique had surreptitiously murdered Joshua and Naomi Collins nearly 200 years before, when heavy pieces of Collinwood's stonework were supernaturally made to crash down upon the family's founding couple.)
The witch transforms the elaborate carvings in the mansion's foyer into animated beings, attacking Barnabas, Elizabeth and others. Eel-like banister decorations slither up the foyer's staircase to attack Elizabeth on the landing. Life-sized wooden Nereid carvings on the walls reach out and ensnare Barnabas to hold him back. Blood begins to cascade from the portraits as the figures therein, brought to life by Angelique's spells, laugh mockingly at the embattled Collins family. Elizabeth, trying to protect herself and others, uses a shotgun to blast some of the attacking figures, but Angelique ultimately can only be defeated by a superior supernatural force.
A fire erupts in Collinwood during this seemingly final battle between Angelique and the Collins family and begins to consume the foyer area of the mansion. Eventually Angelique is defeated, impaled upon the tentacled chandelier in the foyer, which has crashed to the floor. Angelique sinks into apparent death while collapsed against the fallen chandelier.
Despite the victory of the Collins family, the last time Collinwood is seen in the film, the mansion remains ablaze and there is no indication in the film that anyone is attempting to douse the spreading flames. (Collinsport's firefighters are shown in preceding scenes to be already occupied by another fire started by Angelique in the town below.) Most of the escaped survivors of Collinwood look on as their home is engulfed in flame, with Elizabeth vowing the family will "endure."