The King of Elfland's Daughter by Lord Dunsany

Winter descended on Erl and gripped the forest, holding the small twigs stiff and still: in the valley it silenced the stream; and in the fields of the oxen the grass was brittle as earthenware, and the breath of the beasts went up like the smoke of encampments. And Orion still went to the woods whenever Oth would take him, and sometimes he went with Threl. When he went with Oth the wood was full of the glamour of the beasts that Oth hunted, and the splendour of the great stags seemed to haunt the gloom of far hollows; but when he went with Threl a mystery haunted the wood, so that one could not say what creature might not appear, nor what haunted and hid by every enormous bole. What beasts there were in the wood even Threl did not know: many kinds fell to his subtlety, but who knew if these were all?

And when the boy was late in the wood, on happy evenings, he would always hear as the sun went blazing down, rank on rank of the elfin horns blowing far away eastwards in the chill of the coming dusk, very far and faint, like reveillé heard in dreams. From beyond the woods they sounded, all those ringing horns, from beyond the downs, far over the furthest curve of them; and he knew them for the silver horns of Elfland. In all other ways he was human, and but for his power to hear those horns of Elfland, whose music rings but a yard beyond human hearing, and his knowledge of what they were; but for these two things he was as yet not more than a human child.