Flatland was written by Edwin A. Abbott, and published in 1884. Abbott develops a thinner-than-paper world that exists in only two dimensions. He describes the hierarchy within that world, and some of its societal challenges. He then introduces a three-dimensional character, like you and me. The 3-D fellow can easily see the two-D people, but it is very hard for the 2-D people to conceive the full reality of the 3-D character. The book goes on to apply that concept to how 3-D people like us would experience meeting 4-D beings. (In short - very uncomfortably!)

I was happy to find tonight a youtube link to Carl Sagan demonstrating the Flatlander meeting a 3-D apple.