More than 500 years after it was built, Filippo Brunelleschi's dome of Santa Maria del Fiore in Florence, Italy, remains the largest masonry dome ever built. But the dome's construction methods are still a secret, as no plans or sketches have been discovered. The only clue Brunelleschi left behind was a wooden and brick model. While the dome has been plagued by cracks for centuries, new breakthroughs in muon imaging may help preservationists uncover how to save the iconic structure and reveal new ideas on its construction.