'the people who danced on the hill on summer nights'

My favourite Arthur Machen story is the The White People, published in 1899, featuring the diary of a young woman who has stumbled into the world of faery or something similar...

'she told me one very strange story about the hill, and I trembled when I remembered it. She said that people always went there in summer, when it was very hot, and they had to dance a good deal. It would be all dark at first, and there were trees there, which made it much darker, and people would come, one by one, from all directions, by a secret path which nobody else knew, and two persons would keep the gate, and every one as they came up had to give a very curious sign, which nurse showed me as well as she could, but she said she couldn't show me properly. And all kinds of people would come; there would be gentle folks and village folks, and some old people and boys and girls, and quite small children, who sat and watched. And it would all be dark as they came in, except in one corner where some one was burning something that smelt strong and sweet, and made them laugh, and there one would see a glaring of coals, and the smoke mounting up red...

And when they were all inside, round in a ring, touching each other, some one began to sing in the darkness, and some one else would make a noise like thunder with a thing they had on purpose, and on still nights people would hear the thundering noise far, far away beyond the wild land, and some of them, who thought they knew what it was, used to make a sign on their breasts when they woke up in their beds at dead of night and heard that terrible deep noise, like thunder on the mountains. And the noise and the singing would go on and on for a long time, and the people who were in a ring swayed a little to and fro; and the song was in an old, old language that nobody knows now, and the tune was queer. Nurse said her great-grandmother had known some one who remembered a little of it, when she was quite a little girl, and nurse tried to sing some of it to me, and it was so strange a tune that I turned all cold and my flesh crept as if I had put my hand on something dead.

'Philos under a full moon' by Ric Nagualero

Sometimes it was a man that sang and sometimes it was a woman, and sometimes the one who sang it did it so well that two or three of the people who were there fell to the ground shrieking and tearing with their hands. The singing went on, and the people in the ring kept swaying to and fro for a long time, and at last the moon would rise over a place they called the Tole Deol, and came up and showed them swinging and swaying from side to side, with the sweet thick smoke curling up from the burning coals, and floating in circles all around them. Then they had their supper. A boy and a girl brought it to them; the boy carried a great cup of wine, and the girl carried a cake of bread, and they passed the bread and the wine round and round, but they tasted quite different from common bread and common wine, and changed everybody that tasted them. Then they all rose up and danced, and secret things were brought out of some hiding place, and they played extraordinary games, and danced round and round and round in the moonlight, and sometimes people would suddenly disappear and never be heard of afterwards, and nobody knew what had happened to them'.