In The Phantom Tollbooth, it takes a ton of courage for Milo to get in his little car and pass through the Phantom Tollbooth. He knows he's going someplace he's never been to or even heard of before, but this doesn't faze him at all. And once he gets into the Lands Beyond, he faces each new part of it with a pure heart and a clear interest. Our guy is the ultimate explorer. He wants to know more about these unrealistic places, no matter what dangers he might face. He's more interested in each of them than he ever was in the geography or history of "real" places he learned about in school, which begs the question: what is it about the Lands Beyond that has normally-bored Milo itching to see more?
While the kingdoms of Dictionopolis and Digitopolis are interesting and entertaining, the majority of The Phantom Tollbooth's action takes place not in the Kingdom of Wisdom but in the Mountains of Ignorance, because that's where the characters need to do the most exploring (and learning).
If Milo had examined the map that arrived with the tollbooth more carefully, he might not have gone on his journey in the first place.