Children's book from the 90s early 00s about kids discovering a parallel town. Green book cover

Question

I read a book in the late 90s or very early 00s, and I know it had a green cover, crazy green colour with a lot of activity on it too. It was about some kids who discovered this other parallel town or city or something. They were just average kids. I'm not sure on appearance as it's been a very long time since I read it, and I'm not sure if they were young teens or slightly younger. I'd guess between 11-13 years old, but they were just normal kids. I think there was a main male lead and a female who was a kind of sidekick character who ran along with him. I can't remember how they traveled to the town, possibly by touching an object.

The main thing I remember is that when they traveled to this place they still remained in their original place too and would just be like zoned out. And I remember one scene where one of the kids is riding in a car and wanted to do a quick travel there so he does. Also time worked differently, so a second in their actual world was like a day in this discovered world.

I loved it when I was a kid but cannot for the life of me find out what it was. I was around 10ish years old when I read this book.

I hope someone can help! Thanks in advance :)

Answer 1

Try Alan Nourse's The Universe Between, which has a green cover on at least one edition, and is about dimension travelling. From this review:

Ambitious cryogenics research has created an incomprehensible thing in the middle of the lab. Attempts to understand it have killed three men and put two more in the madhouse. Determined to unravel the mystery, Dr. John McEvoy has turned to the Hoffman Center. Perhaps the Center can provide a volunteer resilient enough to survive the thing (which may be a hypercube).

Much to McEvoy’s surprise, the best man for the job is a girl.

Gail Talbot is a survivor. Others might have been broken by her miserable experiences; Gail has learned to adapt and survive. She finds the realm beyond the hypercube too much for even her remarkable mind to understand — but she does manage to survive and return to her home world with a bold plan to explore the universe next door.

....

Gail Talbot, now Gail Benedict, has bequeathed interdimensional exploration to her son Robert. Raised from infancy in both our world and the four-dimensional one next door, Robert can function in both, at least to a degree. He’s never managed to understand the entities on the other side or make himself understood. Now, if humanity is to survive, he must succeed in communicating.

Answer 2

Could it be Elidor?

First published in 1965, I read this 1986 edition in school around 1991/1992.

Roland, Helen, Nicholas and David are lured into a ruined church, where the fabric of time and place is weak enough to allow them into Elidor. It is a world almost destroyed by fear, and the children are charged with guarding its Treasures. But then the evil forces find a way to this world.