Whereupon my muse, impish soul, whispered that what a silly goose he was, assuming that the world is not flat.
To be sure, it might be round, just as it might be flat. There are few tales where it really matters what shape the world is. A man who sets out to flee as far as he can go from his homeland and finds himself back there needs a round world -- and rather remarkable travel abilities to manage it, especially if their knowledge of geography means he doesn't know he has to stop half way to get as far as he can without leaving the globe. When G. K. Chesterton sent his hero to rescue a princess in the Wood Beyond the World's End, where is always twilight, he needed a flat world. Technically, any writer would, as long as you use "World's End" literally. And what's the fun of using it if it's not literal?
To be sure, if you make it flat, you need it to either be an infinite plane, or you need to decide how it ends. Terry Pratchett has it end with an edge; so does C. S. Lewis in Narnia. On the other hand, you could have it end with the sky, perhaps as hard as crystal, or perhaps the water of encircling ocean slowly melts into mist so the edge is a glowing mist that eventually you can't travel through. (A problem with the edge of crystal hardness is what happens when someone tries to go through. Come to think of it, Daphne's imaginary world in The Golden Age tackles that.) I'm playing with the notion of having the world be composed of the four elements mixed in harmony, with them growing more and more elemental the farther you go, so they turn into regions you can't travel for the purity of the element -- an idea inspired by looking at AD&D's cosmology, and throwing things out, including the gates, so that you had only the four elemental planes, and the worlds where they mixed.
Non-Euclidean geography offers even more possibility.
But nothing says it has to be round.