The Capuchin Cemetery in the Church of the Immaculate Conception could easily be missed by any tourist in Rome.  It is not listed as a major sight, it is somewhat macabre; so not everyones will appreciate it. Still, it has its attraction. I actually think I remember seeing, in my youth, a 60 minute documentary on the cemetery.

Note: no photos are allowed in the cemetery. The photos on this page came from Wickimedia Commons (licensing info) .