The Hereford Mappa Mundi is the largest medieval map known to still exist. It is a map drawn up by medieval monks to depict our world, based on myths, legend and the monks imagination of distant lands. Beautiful, but laughably inaccurate based on what we now know the world looks like, particularly in our age of super accurate and detailed satellite mapping; it is based entirely in assumptions rather than facts. An interesting example of the gap between human assumptions and reality.
(Image via Wikipedia)