The House on the Borderland by William Hope Hodgson

And so, after a time, I came to the mountains. Then, the course of my journey was altered, and I began to move along their bases, until, all at once, I saw that I had come opposite to a vast rift, opening into the mountains. Through this, I was borne, moving at no great speed. On either side of me, huge, scarped walls of rocklike substance rose sheer. Far overhead, I discerned a thin ribbon of red, where the mouth of the chasm opened, among inaccessible peaks. Within was gloom, deep and somber, and chilly silence. For a while, I went onward steadily, and then, at last, I saw, ahead, a deep, red glow, that told me I was near upon the further opening of the gorge.

A minute came and went, and I was at the exit of the chasm, staring out upon an enormous amphitheatre of mountains. Yet, of the mountains, and the terrible grandeur of the place, I recked nothing; for I was confounded with amazement to behold, at a distance of several miles and occupying the center of the arena, a stupendous structure built apparently of green jade. Yet, in itself, it was not the discovery of the building that had so astonished me; but the fact, which became every moment more apparent, that in no particular, save in color and its enormous size, did the lonely structure vary from this house in which I live.