In 1975, Paolo Dal Poggetto, then director of the Medici Chapels museum in Florence, stumbled upon a Renaissance treasure.

While searching for a new way for tourists to exit, Dal Poggetto and his colleagues discovered a trapdoor hidden beneath a wardrobe near the New Sacristy, a chamber designed to house the ornate tombs of Medici rulers. Below the trapdoor, stone steps led to an oblong room filled with coal that at first appeared to be little more than storage space.

But on the walls, Dal Poggetto and his colleagues found what they believe are charcoal and chalk drawings from the hand of famed artist Michelangelo. While the room is closed to the public to protect the artwork, National Geographic photographer Paolo Woods was recently granted rare access to capture its remarkable contents. (Also see "What Makes a Genius?" in National Geographic magazine.)

The artwork is visible today because Dal Poggetto took no chances when he first entered the chamber. This being Florence, home to many of history’s towering Renaissance artists, he suspected something valuable might be lurking underneath the layers of plaster. (See “How Do You Find a ‘Lost’ Masterpiece?”)

“When we have very old buildings, we must pay attention,” says Monica Bietti, Dal Poggetto’s successor at the Medici Chapels.

Under Dal Poggetto’s direction, experts spent weeks meticulously removing the plaster with scalpels. As the coating disappeared, dozens of drawings emerged, many of them reminiscent of Michelangelo’s great works—including a marble sculpture of a human figure adorning the tomb of Giuliano de’ Medici in the New Sacristy above, which Michelangelo himself designed.

Dal Poggetto concluded that the artist took cover inside the chamber for about two months in 1530 to hide from the Medici family. A popular revolt had sent the city’s Medici rulers into exile in 1527, and despite their previous patronage of his work, Michelangelo had betrayed the family, aligning himself with fellow Florentines against their rule.

With their return to power a few years later, the 55-year-old artist’s life was in danger. “Naturally, Michelangelo was afraid,” says Bietti, “and he decided to stay in the room.”

Bietti suspects that Michelangelo spent his sequestered weeks taking stock of his life and his art. The drawings on the walls represent works he intended to finish as well as masterpieces he completed years earlier, she says, including a detail from the statue of David (finished in 1504) and figures from the Sistine Chapel (unveiled in 1512).

“He was a genius,” she says, spurred by his boundless creativity. “What can he do there? Just draw.” (Take our quiz: “Do You Have the Traits of a Genius?”)

As with any unsigned, centuries-old artwork, it is impossible to confirm the origins of the drawings with absolute certainty. The consensus seems to be that some of the doodles on the wall are far too amateurish to be Michelangelo’s. But the provenance of the rest of them remains a matter of opinion.

After the 1975 discovery, a prominent Renaissance art authority hailed the collection of sketches as one of the major artistic finds of the 20th century. But William Wallace, a Michelangelo scholar at Washington University in St. Louis, is skeptical.

View Images Flying ... The rough outline of a human figure seems to soar across one wall of the chamber. Photograph by Paolo Woods, National Geographic

View Images Or Falling? The chamber drawing bears a striking resemblance to the central figure in this Michelangelo sketch for "The Fall of Phaeton." Photograph courtesy National Museum of the Academia Galleries of Venice

Wallace believes that Michelangelo was too prominent to have holed up in the lower-level room, and instead he would have been taken in by one of his other patrons. He also suspects that the drawings were completed earlier, some time in the 1520s, when Michelangelo and his many assistants would have taken respites from laying brick and cutting marble for the New Sacristy they were building above.

Several of the drawings might be Michelangelo originals, Wallace says, but others were likely depictions by workers sorting out artistic dilemmas or simply amusing themselves during breaks.

“Separating one from the other is almost impossible,” he says. Still, he adds that the mystery of who crafted the drawings does not take away from their value or the importance of the discovery.

“Being in that room is exciting. You feel privileged,” he says. “You feel closer to the working process of a master and his pupils and assistants.” (Also see pictures by an incredible artist who can draw a whole city from memory.)

The room evokes an emotional response among viewers lucky enough to see it. Standing within its four walls, dimly lit by a small corner window, it’s as if one is peering into the mind of Michelangelo, whose breathtaking artistry fills the building.

“This is a person who had infinite capacity,” says Wallace. “He lived to be 89 years old and never stopped getting better and better.”

View Images Familiar Face This bearded visage appears among the sketches on one chamber wall. Photograph by Paolo Woods, National Geographic

View Images Carved in Marble The sketch looks like a face from the statue "Laocoön and His Sons," a work of ancient art that inspired Michelangelo. Photograph by Eric Vandeville, Gamma-Rapho, Getty Images

View Images Take a Seat One chamber wall bears these sketches of disembodied legs in various poses. Photograph by Paolo Woods, National Geographic