Simplify the following text for a Grade 6 native English-speaking person.
Original: In C. S. Lewis ' The Voyage of the Dawn Treader the fictional world of Narnia is `` round like a table '' ( i.e. flat ) , not `` round like a ball '' , and the characters sail toward the edge of this world ( although , in Lewis ' subsequent Narnian novel The Silver Chair , the Earth itself is accepted and written as being spherical , with Narnian king Caspian X being amazed by this fact ) .
Simplified: In C. S. Lewis ' The Voyage of the Dawn Treader the fictional world of Narnia is `` round like a table '' ( i.e. , flat ) , not `` round like a ball '' , and the characters sail toward the edge of this world .