This book was written for children, however it has found much acclaim amongst adults across the world. It was originally serialized on the podcast show KidsCastSciFi. It follows the adventures of two boys who accidentally discover some form of gateway, that takes them to other worlds or parallel universes. This was the book that started a series (The Tower Bridge being the next in line). Enjoy.
Author's Website : http://SciFiStories.co.uk