3. Babylon
This is an example of the aforementioned Doctor Who gold that has barely been touched. The only time Babylon, or anything that has to do with Mesopotamia, was ever featured by Doctor Who was in a short story featuring the Ninth Doctor. However, this is a city worth so much more than one little short story. There are multiple sites that could even be visited, like the Hanging Gardens. Imagine the Doctor walking through the Ishtar Gate. This could potentially be a wonderful episode because there is so much to dig up in Babylon. Even if there isn't an episode in Babylon, there should be one in Mesopotamia. There could be a huge moral questioning on the Code of Hammurabi (an eye for an eye, a tooth for a tooth...) and the invention of the wheel might be funny if it was included in the episode. There is really so much to play with in Babylon and Mesopotamia. Maybe even something involving the mythology of the Tower of Babel?