The story we ended up choosing as a theme for this project was The Dreams in the Witch House. The story deals with a mathematics student retracing the steps of the colonial-era witch whose house he's renting a room in, eventually discovering that high-order calculus equations can be used to access strange dimensions inhabited by horrifying things. Then things get weird.
He knew his room was in the old Witch-House - that, indeed, was why he had taken it. There was much in the Essex County records about Keziah Mason's trial, and what she had admitted under pressure to the Court of Oyer and Terminer had fascinated Gilman beyond all reason. She had told Judge Hathorne of lines and curves that could be made to point out directions leading through the walls of space to other spaces beyond, and had implied that such lines and curves were frequently used at certain midnight meetings in the dark valley of the white stone beyond Meadow Hill and on the unpeopled island in the river. She had spoken also of the Black Man, of her oath, and of her new secret name of Nahab. Then she had drawn those devices on the walls of her cell and vanished...
He studied the timber and plaster walls for traces of cryptic designs at every accessible spot where the paper had peeled, and within a week managed to get the eastern attic room where Keziah was held to have practised her spells. It had been vacant from the first - for no one had ever been willing to stay there long - but the Polish landlord had grown wary about renting it. Yet nothing whatever happened to Gilman till about the time of the fever.
The goal for the decorations is to incorporate as many elements and themes of the story as possible into a static display space, rather than trying to recreate a single location faithfully as described. The basic backdrop, then, is the decrepit attic room that Gilman rooms in, but since a decrepit room all on its own isn't that scary we'll be trying to toss a few more things in:
Toward the end of March he began to pick up in his mathematics, though the other stndies bothered him increasingly. He was getting an intuitive knack for solving Riemannian equations, and astonished Professor Upham by his comprehension of fourth-dimensional and other problems which had floored all the rest of the class. One afternoon there was a discussion of possible freakish curvatures in space, and of theoretical points of approach or even contact between our part of the cosmos and various other regions as distant as the farthest stars or the transgalactic gulfs themselves - or even as fabulously remote as the tentatively conceivable cosmic units beyond the whole Einsteinian space-time continuum. Gilman's handling of this theme filled everyone with admiration, even though some of his hypothetical illustrations caused an increase in the always plentiful gossip about his nervous and solitary eccentricity. What made the students shake their heads was his sober theory that a man might - given mathematical knowledge admittedly beyond all likelihood of human acquirement - step deliberately from the earth to any other celestial body which might lie at one of an infinity of specifc points in the cosmic pattern.
...
For some time, apparently, the curious angles of Gilman's room had been having a strange, almost hypnotic effect on him; and as the bleak winter advanced he had found himself staring more and more intently at the corner where the down-slanting ceiling met the inward-slanting wall. About this period his inability to concentrate on his formal studies worried him considerably, his apprehensions about the mid-year examinations being very acute. But the exaggerated sense of bearing was scarcely less annoying. Life had become an insistent and almost unendurable cacophony, and there was that constant, terrifying impression of other sounds - perhaps from regions beyond life - trembling on the very brink of audibility.
...
But it was not in these vortices of complete alienage that he saw Brown Jenkin. That shocking little horror was reserved for certain lighter, sharper dreams which assailed him just before he dropped into the fullest depths of sleep. He would be lying in the dark fighting to keep awake when a faint lambent glow would seem to shimmer around the centuried room, showing in a violet mist the convergence of angled planes which had seized his brain so insidiously. The horror would appear to pop out of the rat-hole in the corner and patter toward him over the sagging, wide-planked floor with evil expectancy in its tiny, bearded human face; but mercifully, this dream always melted away before the object got close enough to nuzzle him. It had hellishly long, sharp, canine teeth; Gilman tried to stop up the rat-hole every day, but each night the real tenants of the partitions would gnaw away the obstruction, whatever it might be. Once he had the landlord nail a tin over it, but the next night the rats gnawed a fresh hole, in making which they pushed or dragged out into the room a curious little fragment of bone.
...
Something in the air of the hoary town worked obscurely on his imagination. The professors at Miskatonic had urged him to slacken up, and had voluntarily cut down his course at several points. Moreover, they had stopped him from consulting the dubious old books on forbidden secrets that were kept under lock and key in a vault at the university library. But all these precautions came late in the day, so that Gilman had some terrible hints from the dreaded Necronomicon of Abdul Alhazred, the fragmentary Book of Eibon, and the suppressed Unaussprechlicken Kulten of von Junzt to correlate with his abstract formulae on the properties of space and the linkage of dimensions known and unknown.