From the NY Times:
The number of visitors to the Vatican has nearly doubled in the last 10 years, hitting a high of 4.2 million in 2006, and has resulted in the overcrowding of a structure originally built to accommodate a Renaissance papal court, not up to 20,000 visitors at a time shuffling around one another.
Between enormous tour groups and rowdy school-trippers, a visit to the Vatican Museums can become “more of a traumatic than an artistic experience for tourists,” said Paola, one of several guides who were interviewed and who asked that their full names not be used for fear of offending the Vatican.
