The Prophecy by Jeffrey Poole

After learning they’ve inherited property from reclusive grandparents he hardly knew, Steve and Sarah Miller decide to take a few days off to investigate their newfound fortune in the quiet Idaho resort town of Coeur d’Alene. The inheritance turns out to be beyond their wildest dreams, a vast mansion with lovely gardens. While exploring, they discover a unique set of carved doors on the top floor of their new home. Disguised as a simple door, a portal is accidentally activated and Steve and Sarah find themselves staring at the amazing sight of a lush forest beyond. It’s a tantalizing decision: to check it out or to run. Curiosity getting the better of them, they step through, the portal disappears, and they are on a one-way journey to a land where people have strange powers and where mythical creatures abound.