SOLVED. Portal Fantasy Middle Grade or YA- The magic has faded from the world but you can enter the magical world either by entrances in hills or train stations? [s]

[Mpnaturelover]

So I read this book when I was in middle school- so sometime around 2005-2010. The book did not seem new, maybe printed in the 90s? Or I could have just borrowed a well loved copy.
I don't have a good memory of what time period it takes place in because it spends most of the time in the fantasy world. But it used to be easier to get to the fantasy world but modern invention has changed things so probably 1960s or beyond. To get to the fantasy world you walk through entrances in hills or a coat room in a train station. There is a troll character in the fantasy world who has grass hair. I want to say that either the children who cross into the world are supposed to rule the fantasy world Narnia style, Or they meet children who are the heirs to the throne/will come into power. At one point they see a fleet of ships coming for them but I can't remember if they were the good guys or the bad guys
I can honestly remember the cover with way more detail so I'll describe that as well. There are several people standing in the bottom right corner. One of the characters is I think a troll who has spiky grass for hair. There is a grassy hobbit hole style hill in the middle ground and a sparkling ocean in the background. There is a vaguely art nouveau border that kind of looks like an old fashioned train station.

I'm sorry that I don't have more information, its been a long time!

[Rainbowheart]

The Secret of Platform 13

[Mpnaturelover]

YES Thank you so much- my mind can finally rest easy

[Rainbowheart]

Great, glad to help out!