Archie's Mirror - Turner Geoff

Staring up at his bedroom ceiling, the shadows began to form shapes before his eyes. Archie imagined the shapes were lands; different islands on a faraway map. He imagined knights galloping across green fields, horses’ hooves cutting through the mist. On one side was a forest, a terrifying forest of smoke, full of mystery and darkness. Across the middle was a sea, but a sea like no other. A solid sea of frozen waves many adventurers had tried, but failed, to cross. Then there was a great desert of moon sand that glowed blue both day and night. And further still were the rocky crystal peaks of the Mountains of Ice and Tears. Hidden deep amongst them was a palace and inside there–
well, inside there was a terrible secret.

One night Archie discovers a gateway to another world and the ability to travel by mirror. Once in the Land Beyond, he embarks on a fantastic adventure, befriending giants, battling monsters, and facing a great evil that threatens to destroy the kingdom.