Hi all... I'm looking for the title of my favorite childhood book. All I can remember is was a story about boy, (I think his name may have been Alex but count on that!) that receives a package & it's a kind of door into another world where's Kings of these two (?) worlds/kingdoms, there's a place called the doldrums & it's a wonderful book. It was also made into a film. I guess it'd be from the 60's or 70's as I'm getting on a bit now! Thanks!

The Phantom Tollbooth?

I googled it and it is definitely the Phantom Tollbooth.