Through the Gates of the Silver Key by H.P. Lovecraft

As the Hindoo paused in his story he saw that de Marigny and Phillips were watching him absorbedly. Aspinwall pretended to ignore the narrative and kept his eyes ostentatiously on the papers before him. The alien-rhythmed ticking of the coffin-shaped clock took on a new and portentous meaning, while the fumes from the choked, neglected tripods wove themselves into fantastic and inexplicable shapes, and formed disturbing combinations with the grotesque figures of the draft-swayed tapestries. The old negro who had tended them was gone -- perhaps some growing tension had frightened him out of the house. An almost apologetic hesitancy hampered the speaker as he resumed in his oddly labored yet idiomatic voice.

"You have found these things of the abyss hard to believe," he said, "but you will find the tangible and material things ahead still harder. That is the way of our minds. Marvels are doubly incredible when brought into three dimensions from the vague regions of possible dream. I shall not try to tell you much -- that would be another and very different story. I will tell only what you absolutely have to know."