One of the great architectural treasures of New York City is underground.
The old City Hall subway station has been shuttered for 70 years and left to collect dust in the dark - even with its majestic arches and chandeliers that rival any cathedral.
It was one of the many structures built by the Guastavino family and is now being celebrated in a wondrous exhibit at the Museum of the City of New York "Palaces for the People."
"When it opened it was called the Mona Lisa of subway stations," said John Ochsendorf, a professor at the Massachusetts Institute of Technology and curator of the exhibit. He's dazzled by the marriage of beauty and function in Guastavino's work.
"This is absolutely awe inspiring as a work of technology, but also as a work of art. I'm an engineer, but I struggle to explain how this stands up."
The Guastavinos were Spanish immigrants who brought centuries-old Mediterranean techniques to the U.S. in the late 1800s. They used a technique called "thin-tile vaulting" to create a signature and patented style.
It was inexpensive, lightweight and strong. And even more important at the turn of the century, it was fireproof.
"Most American cities were originally built of wooden structures and sometimes there would be a fire that could burn tens of thousands of buildings at once," Ochsendorf said.
The Guastavinos designed the Oyster Bar at Grand Central Station. A fire in 1997 destroyed some of the tiles, but the structure remained intact.
In all, their domes, arches and vaulted ceilings grace more than 250 buildings in New York City - like the Ellis Island registry room and the Cathedral of St. John the Divine in Harlem. But there are many more that are still undiscovered.
"I have a standing offer: if anyone finds a Guastavino building that I don't know about, I will buy you lunch," Ochsendorf said.
Ochsendorf has been on a scavenger hunt for these sites for years and recently experienced the realization of a lifelong dream, traveling by train for a private tour of the underground treasure that is the old City Hall station, hidden for decades in the heart of New York City.
"I have a dream that someday, it could be reopened either as a station, or a museum," he said.