Gilman’s room was of good size but queerly irregular shape; the north wall slanting perceptibly inward from the outer to the inner end, while the low ceiling slanted gently downward in the same direction. Aside from an obvious rat-hole and the signs of other stopped-up ones, there was no access—nor any appearance of a former avenue of access—to the space which must have existed between the slanting wall and the straight outer wall on the house’s north side, though a view from the exterior shewed where a window had been boarded up at a very remote date. The loft above the ceiling—which must have had a slanting floor—was likewise inaccessible. When Gilman climbed up a ladder to the cobwebbed level loft above the rest of the attic he found vestiges of a bygone aperture tightly and heavily covered with ancient planking and secured by the stout wooden pegs common in colonial carpentry. No amount of persuasion, however, could induce the stolid landlord to let him investigate either of these two closed spaces.
As time wore along, his absorption in the irregular wall and ceiling of his room increased; for he began to read into the odd angles a mathematical significance which seemed to offer vague clues regarding their purpose. Old Keziah, he reflected, might have had excellent reasons for living in a room with peculiar angles; for was it not through certain angles that she claimed to have gone outside the boundaries of the world of space we know? His interest gradually veered away from the unplumbed voids beyond the slanting surfaces, since it now appeared that the purpose of those surfaces concerned the side he was already on.
— H.P. Lovecraft: Dreams in the Witch House