Then she went to sleep, to dream the strange dreams of herl lineage, things too fantastic to be worth recording, for she was at the time of life when a girl's thoughts turn to fantasy, even beyond Athroonagh, and here in Athroonagh her fantasies had strange tales amongst which to riot.
This is from "The Story of Mona Sheehy" by Lord Dunsany in 1939.
I can't understand the meaning of the sentence below.
strange tales amongst which to riot.
I am glad if somebody would kindly teach me.