I think Chichen Itza is a super fascinating topic within the Middle Ages timeline as it is outside of the general scope that people think of when they think of the Middle Ages. It is a city of the Mayan and Toltec culture in the Americas and is largely separated from the rest of the world and its influence so it is really interesting to see in what ways they advanced and what inspired them in contrast to the rest of the world.
An extremely important point, and seemingly a good source for a thesis. This city not only expands what we know about the Middle Ages, but also acts as a present day influence of the time.