The Dreams in the Witch House is a novelette written by H. P. Lovecraft, part of the Cthulhu Mythos genre of horror fiction. Written in January/February 1932, it was first published in Weird Tales, July 1933.
Walter Gilman, a student of mathematics and folklore at Miskatonic University, takes a room in the Witch House, a house in Arkham thought to be accursed. The first part of the story is an account of the history of the house, which has once harboured Keziah Mason, an accused witch who disappeared mysteriously from a Salem jail in 1692. Gilman discovers that for the better part of two centuries many if not most of its occupants have died prematurely.
The dimensions of Gilman's room in the house are unusual, and seem to conform to a kind of unearthly geometry that Gilman theorizes can enable travel from one plane or dimension to another. In his dreams Gilman is taken to a city of Lovecraft's "Elder Things", and even brings back tangible evidence that he's actually been there. Several times his dreaming self encounters a bizarre "congeries of iridescent, prolately spheroidal bubbles", as well as a trapezoidal figure, both of which seem sapient. It is hinted that these may be the extra-dimensional forms of Keziah and her familiar.
Of much more direct concern, however, are Gilman's nightly dream sojourns with the old hag Keziah Mason and her rat-bodied, human-faced familiar Brown Jenkin, sojourns which he increasingly believes are actually happening in the real world. One night, Gilman dreams Keziah, Brown Jenkin, and the infamous "Black Man" force him to be an accomplice in the kidnapping of an infant. He awakes to find mud on his feet and news of the kidnapping in the newspaper.
On May Eve (Walpurgis Night), Gilman dreams that he thwarts Keziah from sacrificing the baby, only to have it killed by Brown Jenkin. Coming back to wakefulness in this plane, Gilman hears an unearthly cosmic sound that leaves him deaf. The next morning, Gilman is found dead in his room in the Witch House, a hole burrowed through his chest and his heart eaten out.
The landlord then abandons the house completely, and when it is finally demolished years later, a space between the walls is found filled with children's bones, a sacrificial knife, and a bowl made of some metal that scientists are unable to identify. A strange stone statuette of a star-headed "Elder Thing" is also found, and these items go on display in the Miskatonic University museum, where they continue to mystify scholars.