Pretty much everything that you really need to know about paganism, you can learn from the novels of Rosemary Sutcliff.
Thanks to her, I—a little tow-headed kid in suburban 1960s Steeltown, USA—grew up knowing about Samhain and Beltane, Horned Gods and Kings who Die for Corn. Each year at Samhain, I pour to her hallowed memory.
Recently, rereading her novel The Lantern Bearers, I came across a poem in which a Woman of the Other Side, one of the Undying, the Lordly Ones, calls from That Land, the Land of Youth, to a mortal listener here in our world. In the haunting images and bright enameled colors of the Celtic Otherworld, she calls, and the birds of Rhiannon sing.
Song of the Woman of the Sidhe
To Oisín*
The apple tree blooms white
in the Land of the Living;
the shadow of the blossom
falls across my door stone:
a bird flutters in the branches, singing.
Green is my bird
as the green earth of men,
his song is forgetfulness.
Listen, and forget the earth.