The Bored Book by David Michael Slater, illustrated by Doug Keith

From chapters.ca:
A brother and sister are bored and irritated visiting their grandfather. There's no TV, no video games or computers - only books! Sent by their grandfather into the attic, they discover a dusty volume that is unlike all the others. When they open it, it expands into a giant map. As the map grows larger and larger, filling the attic, the children fall into adventures that take them all over the world, face to face with sharks, pirates, knights, even an abominable snowman. Suddenly their visit is anything but boring! The Bored Book uses stunning illustrations, with no text, to remind youngsters of the unique adventures to be found in books.