September 10, 2021 3:53 PM EDT

Filmmaker Joshua Charow spent one evening documenting the work of James Maroon and his colleagues who clean the massive reflecting pools at the 9/11 Memorial every night.

Each nearly one acre in size, the pools mark the original footprints of the twin towers and are the centerpieces of the memorial. They opened to the public a decade ago. Charow, who filmed and directed this story in collaboration with the Alliance for Downtown New York and Josh Katz, told TIME the crew mostly cleans up leaves, although occasionally other items, such as cameras and jewelry, fall in.

The view from the bottom is striking, he explains: “The walls are 30 feet high. It feels like you’re in a canyon. While the pools are being cleaned, the waterfalls are turned off as you can see in the film. However, when we first got into the pool Anthony LoCasto, the chief engineer of the memorial, made a call on his walkie. Within a few minutes the waterfalls started pouring down around us. It was spectacular to be at the bottom of this memorial, surrounded by four, 30-foot waterfalls. Despite having done this many times over the years, you could see how it affects Anthony as well. He knew this was a special experience, regardless of how many times he’s seen it.”

Twenty years after the attacks, Charow’s video honors the poignant anniversary as well as the resilience of a city and its workers who continue to remember what was lost on that day.

“Maintaining these incredibly important landmarks in our city requires a remarkable amount of devotion and hard work from a small group of individuals to make sure that this memorial looks flawless for the families that come to see it,” Charow says.

Justine Simons

Contact us at letters@time.com.

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