A quirky art installation featuring 650,000 plastic balls is breathing new life into a dingy and long-forgotten former underground trolley station in the heart of the US capital.
Through June 1, the expanse below Washington's bustling Dupont Circle is being transformed into a hands-on show where visitors young and old can get creative.
"They invite you to build your own thing and to make it interactive," said Holly Joseph, who came in from the suburbs to check it out and leave her mark.
The installation uses white translucent balls from a popular previous one at Washington's National Building Museum. They have been repurposed into bricks of sorts.
With velcro, visitors can stack the cubes and let their building imaginations run wild.
The Dupont Underground, a non-profit, launched a competition to transform the venue into "an unexpected experience."
Some 153 candidates from 19 countries took part, with New York architecture and design studio Hou de Sousa submitting the winning proposal. The studio is a collaboration between Jia Min Nancy Hou and Josh de Sousa.
With the tracks exposed as a reminder of years past, Hou de Sousa assembled the bricks in a semi-circle and in huge columns. The public part is located in the open, central area.
The creations -- a large face mounted on a wall, a princely palace, an arch -- are immortalized on smartphones before being destroyed by their creators or other visitors.
"We proposed a reusable system rather than a specific form or design, resulting in a dynamic and direct relationship between creation and destruction," Hou de Sousa said of their "Raise/Raze" concept.
The installation -- put on in partnership with the nearby Phillips Collection modern art museum among others -- conjures up the Minecraft video game and life-size Legos.
But Dupont Underground's art director Craig Cook prefers a beach analogy.
"It's like the buckets that kids put sand in and then they make shapes," he told AFP.
"The beach" was the theme of last year's installation at the National Building Museum, in which visitors -- including families -- could go plunge into the balls for improvised swims.
The installation isn't widely publicised, with no address or hours online and the entrance off Dupont Circle resembling a subway station.
That could be because only 49 people are allowed in the space at any given time.
Opened in 1949, the trolley station closed in 1962 when the streetcar system shut down. It has largely been empty since, attracting the homeless in the 1960s and briefly hosting a food court in the mid-1990s.
In late 2014, Dupont Underground signed a five-year lease with the city "to permanently redevelop the entire site as a mixed-use cultural destination."
The organisation, in envisioning a future for the space, points to New York's High Line, elevated tracks in the Big Apple that have been transformed into a popular outdoor destination, as an example of the type of urban revitalization it espouses.
With money tight, visitors are asked to pay an entrance fee.
"We hope to generate enough funding to make a bunch of improvements to this space," Cook said.
"It means a lot of work. We don't have any plumbing, we don't have any bathrooms, we don't have any doors."
Looking ahead to the fall, Cook hopes to bring smaller music and cinematography installations to the venue.
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