After years of criticism, this week the curtain was raised on a drastically improved and better protected Sistine Chapel, through innovative lighting and a bold new air exchange system that will reduce the pollution caused by 6 million visitors a year. Never have its 2,730 square yards of precious wall and ceiling frescoes by Michelangelo, Pinturicchio, Botticelli, Ghirlandaio and other great artists been seen in all their stunning glory.