The Vatican Museums started as only one marble sculpture in 1506.
It was purchased more than 500 years ago by a pope, and many more collections and sculptures have been added over the course of its history.
The 16th century was full of mysteries, but perhaps one of the greatest mysteries of all was the lost paintings by Renaissance master Raphael Sanzio da Urbino.
The Italian painter is famously known for being an architect of the High Renaissance.
Raphael's work is admired for its immaculate clarity and composition.
"The way the paintbrush moves," Vatican restorer Fabio Piacentini expressed about Raphael's talents, "even the subtlety of the point of the brushes used to create the small wisps of hair."
In 1508, he was commissioned by a pope to paint his private apartments, which is known today as "Raphael rooms."
Two masterpieces, which are believed to be Raphael's last works before his death at the age of 37, were thought to have been lost forever, but they've been actually hiding in plain site all this time.
During the restoration and cleaning of a room inside the Vatican Museums, ultra-violet and infrared photographs were taken off the walls that unveiled the paintings.
The female allegorical figures of "Freedom" and "Justice," which are depicted on the walls of the Room of Constantine in the papal apartments, are believed to be the work of the 16th century master painter.
The experts were convinced by the distinct brushstrokes that the paintings were the work of Raphael.
Here's a close-up, detailed image of the discovered paintings.
Barbara Jatta, the head of the Vatican Museums, said the restoration of the whole room will take them at least five more years.
"It's one of the most important projects of the last decades - apart from the Sistine Chapel - done in the Vatican Museums."
The Museums's restorers and other experts are unsure that they're any other hidden treasures on the walls of the Vatican, but they said they'll be keeping their eyes open.
"That's the beautiful thing of different projects," Jatta said. "We are still searching...it never ends."