Complex sentence: As with "Flatland" itself, the Flatlanders' encounter with the third dimension are intended to encourage consideration of how higher dimensions would appear to us-specifically, the concept that the universe is the three-dimensional surface of a four-dimensional hypersphere.
Split into simpler sentences: As with "Flatland" itself, the Flatlanders' encounter with the third dimension are intended to encourage consideration of how higher dimensions would appear to us. In this case, specifically the concept that the universe is the three-dimensional surface of a four-dimensional hypersphere.