Quote from : The Voyage of the Dawn Treader Book

Do you mean to say," asked Caspian, "that you three come from a round world (round like a ball) and you've never told me! It's really too bad for you. Because we have fairy-tales in which there are round worlds and I have always loved them … Have you ever been to the parts where people walk about upside-down?" Edmund shook his head. "And it isn't like that," he added. "There's nothing particularly exciting about a round world when you're there.