Fantasy story with a pair of children who travel between two parallel Earths

Question

I have no idea about the age of this book, only that it can't be all that new. I read it at around the age of ten, which would be 30 years ago.

In the story there was a boy and a girl (if I recall correctly) that were enabled somehow (sadly I can't remember) to shift between two parallel versions of Earth. One was our world and one was a kind of desolate wasteland which was inhabited by frightening monsters.

Locations in the two worlds were mirrored, so that what might be a factory in our world was perhaps a castle in the other world. This enabled them to get into locations that were inaccessible in one world by getting into the "mirror" location and then shifting.

I only really remember one powerful scene where one child is cornered by a horse like monster with a skull head and is about to be captured, but the child shifts to our world and finds the monster is a horse skull mounted on a post.

Answer 1

Realise this is an old question, but was looking for the same book myself and finally found it!

The Edge of the World by John Gordon

This review covers the details of the question.

The Edge of the World is a YA fantasy novel first published in 1983. It primarily tells the story of Tekker and his friend Kit, who discover that through moving small objects with their minds (telekinesis) they are able to open up a parallel dimension in the English Fenlands. However, the parallel world is far from being a marsh, but is a burning-hot barren red desert from which ‘horseheads’ emerge. These nightmarish creatures have empty horses skulls, but walk upright on two legs.

Although they are warned not to open the parallel dimension by an old man who once went there and lost what was dearest to him, Kit and Tekker are forced to do so when the controller of the horseheads, a reclusive local woman, harms the mind of Kit’s brother, Dan, and he slips into a coma-like state and then nearer and nearer to death. The only way to undo the damage is to restore a key artifact to the possession of someone who is imprisoned beyond the desert.

The scene where the horse skull creature becomes something else in their world:

Kit understood before Tekker. She saw the rag hanging from the nail beside the doorway, and beyond it, through panes of broken, dusty glass, the thin branches of a dead tree which caught the breeze and flickered across the sky. They were the Horsehead's arms; its skull was the rag.