The Dark Is Rising sequence by Susan Cooper

Fantastical middle grade series set in Cornwall and Wales, spanning thousands of years of history and lore from the region. Cooper's writing is charming, brooding and mysterious, much emulating the landscape. Her deep respect for children and their intelligence is reflected in her careful construction of the main characters. Fun, epic, heartbreaking and clearly the inspiration for a whole generation of YA fantasy novels. Linking the audiobooks here because they are also an incredible listen.