Since night-gaunts are a product of Lovecraft's childhood nightmares and jumbled memories of Gustave Doré's illustrations of Paradise Lost, here's a good excerpt from The Dream-Quest of Unknown Kadath and some of Doré's illustrations.
But dusk was now thick, and the great carven face looked down even sterner in shadow. Perched on that ledge night found the seeker; and in the blackness he might neither go down nor go up, but only stand and cling and shiver in that narrow place till the day came, praying to keep awake lest sleep loose his hold and send him down the dizzy miles of air to the crags and sharp rocks of the accursed valley. The stars came out, but save for them there was only black nothingness in his eyes; nothingness leagued with death, against whose beckoning he might do no more than cling to the rocks and lean back away from an unseen brink. The last thing of earth that he saw in the gloaming was a condor soaring close to the westward precipice beside him, and darting screaming away when it came near the cave whose mouth yawned just out of reach.
Suddenly, without a warning sound in the dark, Carter felt his curved scimitar drawn stealthily out of his belt by some unseen hand. Then he heard it clatter down over the rocks below. And between him and the Milky Way he thought he saw a very terrible outline of something noxiously thin and horned and tailed and bat-winged. Other things, too, had begun to blot out patches of stars west of him, as if a flock of vague entities were flapping thickly and silently out of that inaccessible cave in the face of the precipice. Then a sort of cold rubbery arm seized his neck and something else seized his feet, and he was lifted inconsiderately up and swung about in space. Another minute and the stars were gone, and Carter knew that the night-gaunts had got him.
They bore him breathless into that cliffside cavern and through monstrous labyrinths beyond. When he struggled, as at first he did by instinct, they tickled him with deliberation. They made no sound at all themselves, and even their membraneous wings were silent. They were frightfully cold and damp and slippery, and their paws kneaded one detestably. Soon they were plunging hideously downward through inconceivable abysses in a whirling, giddying, sickening rush of dank, tomb-like air; and Carter felt they were shooting into the ultimate vortex of shrieking and daemonic madness. He screamed again and again, but whenever he did so the black paws tickled him with greater subtlety. Then he saw a sort of grey phosphorescence about, and guessed they were coming even to that inner world of subterrene horror of which dim legends tell, and which is litten only by the pale death-fire wherewith reeks the ghoulish air and the primal mists of the pits at earth’s core.
At last far below him he saw faint lines of grey and ominous pinnacles which he knew must be the fabled Peaks of Thok. Awful and sinister they stand in the haunted dusk of sunless and eternal depths; higher than man may reckon, and guarding terrible valleys where the bholes crawl and burrow nastily. But Carter preferred to look at them than at his captors, which were indeed shocking and uncouth black beings with smooth, oily, whale-like surfaces, unpleasant horns that curved inward toward each other, bat-wings whose beating made no sound, ugly prehensile paws, and barbed tails that lashed needlessly and disquietingly. And worst of all, they never spoke or laughed, and never smiled because they had no faces at all to smile with, but only a suggestive blankness where a face ought to be. All they ever did was clutch and fly and tickle; that was the way of night-gaunts.
As the band flew lower the Peaks of Thok rose grey and towering on all sides, and one saw clearly that nothing lived on that austere and impassive granite of the endless twilight. At still lower levels the death-fires in the air gave out, and one met only the primal blackness of the void save aloft where the thin peaks stood out goblin-like. Soon the peaks were very far away, and nothing about but great rushing winds with the dankness of nethermost grottoes in them. Then in the end the night-gaunts landed on a floor of unseen things which felt like layers of bones, and left Carter all alone in that black valley. To bring him thither was the duty of the night-gaunts that guard Ngranek; and this done, they flapped away silently. When Carter tried to trace their flight he found he could not, since even the Peaks of Thok had faded out of sight. There was nothing anywhere but blackness and horror and silence and bones.