Phantom Tollbooth by Norton Juster

This is the journey of Milo, a boy bored of basically everything around him. One day he receives a mysterious package that turns out to be a tollbooth. For lack of anything better to do, he puts it together and begins to play, only to find himself driving in an entirely different world. There he meets all sort of curious creatures, from a giant watchdog (literally, a dog whose body is a watch) and a humbug the size of a person. Juster plays with words as if they were tangible objects to juggle, and continually surprises the reader by turning ordinary events into magical occurrences. This book very much exemplifies the quote "The Universe is full of magical things patiently waiting for our wits to get sharper" Eden Phillpots."

As most adult readers I read this as a child but it didn't make much of an impression of me at the time so it was great fun to read it as an adult and rediscover it. Utterly delightful.