The Alden Room houses many treasures, including a pirated edition of Diderot's Encyclopédie, the 18th century Enlightenment masterpiece. If you are interested in seeing this 39-volume set firsthand, contact Heather Stalter to arrange for an appointment.
Milne Library has a plethora of information about the Encyclopédie. From the Sources tab to the left, you will find websites, articles, and books related to the Encyclopédie, Diderot, and the Enlightenment. Though not exhaustive, these sources will give you a good start in your own path to enlightenment about the Encyclopédie.