Across the square from the Camposanto is the Sinopie Museum. This museum houses the full-scale sketches that were used to create the frescoes inside the Camposanto. Although it probably receives even fewer visitors than the Camposanto, the museum is certainly a valuable part of your trip to Pisa.
Perhaps the idea of looking at someone’s “rough drafts” sounds boring but I would disagree. The sketches provide a rare insight into the creative process of great works of art. I had fun imagining the corrections and little changes that took place as the art progressed to finished product. The museum itself isn’t huge and can be seen in 30-60 minutes depending upon how much time you spend at each work.
While we were there, the museum had a temporary display of recreated clothing reflecting the attire shown in the frescoes and sketches. This was a nice bit of icing on the cake.