Even as he realised this thing, Carter noticed a change in the course of the helplessly wind-sucked party. They were rising abruptly now, and it was plain that the focus of their flight was the onyx castle where the pale light shone. So close was the great black mountain that its sides sped by them dizzily as they shot upward, and in the darkness they could discern nothing upon it. Vaster and vaster loomed the tenebrous towers of the nighted castle above, and Carter could see that it was well-nigh blasphemous in its immensity. Well might its stones have been quarried by nameless workmen in that horrible gulf rent out of the rock in the hill pass north of Inquanok, for such was its size that a man on its threshold stood even as an ant on the steps of earth's loftiest fortress. The pshent of unknown stars above the myriad domed turrets glowed with a sallow, sickly flare, so that a kind of twilight hung about the murky walls of slippery onyx. The pallid beacon was now seen to be a single shining window high up in one of the loftiest towers, and as the helpless army neared the top of the mountain Carter thought he detected unpleasant shadows flitting across the feebly luminous expanse. It was a strangely arched window, of a design wholly alien to earth.