The Complete Danteworlds: A Reader's Guide to the Divine Comedy (2009).
This is a thorough, interactive map of the stages of Dante's journey. Includes text, art, and audio.
This is a very thorough site about the Chartres Cathedral. The "Learn and Reconstruct" section has many interactive panoramas and pictures, and the "About the Project" link gives a lot of historical information about the cathedral.
This web site discusses art in the Byzantine era and in the Basilica of San Vitale to give a broader sense of how this mosaic fits in to its time and culture.
This is a book writen by Girolamo Bartolomeo Piazza, a judge for the Inquisition in France. This link takes you to the page where he begins describing specific trials he led.
This is a great description of the Ziggurat by a U.S. platoon leader who visited the site. For additional insight into the Ziggurat, watch this slide show with some nice, loud background music: http://www.youtube.com/watch?v=XnWpBwmi6_o