Visitors to the National Building Museum can swim in an ocean of 1 million plastic balls at “The Beach,” an installation in the museum's Great Hall. (Noah Kalina)

Normally, a sea of plastic would sound like a bad thing, such as trash bags and old water bottles floating in polluted water.

But the National Building Museum has turned the idea into something good. The sea is actually a giant plastic ball pit for you to play in.

As part of its annual summertime installation, the Building Museum is bringing the beach to Washington. The indoor exhibit in the museum’s Great Hall is made up of an “ocean” ball pit, a 50-foot shoreline covered in beach chairs and umbrellas, and a snack bar from the folks at Union Kitchen.

The inspiration for creating an indoor beach came from wanting to bring a classic American summertime activity to the city. The design, by architecture firm Snarkitecture, aimed to create a simple indoor version of a typical beach experience.

“You can jump off the pier, have a snack, hang out in a chair and read a book,” said Snarkitecture co-founder Alex Mustonen. “Basically what you would do at the beach.”

Sarah Smith, 4, of Washington plays in the pit of plastic balls during a preview last week for "The Beach." (Sarah Polus/The Washington Post)

Besides everyday fun, every Wednesday “The Beach” will stay open until 9 p.m., and the museum will offer scavenger hunts, live music, tours and games. There are even plans for volleyball.

It took only two weeks to build the indoor beach, even though the pit holds about 1 million balls.

And, Mom won’t yell at you for swimming in the deep end. “You can’t really reach the bottom” of the ball pit, Mustonen said.

However, like in a real ocean, getting around can be tough. “They have this density that makes it so you can’t really walk or stand in them,” Mustonen said of the balls. They create a similar feeling of wading into the ocean with waves crashing around you.

If you’re afraid of germs, don’t worry! The balls are antimicrobial, meaning they kill 99 percent of germs, according to Emma Filar, who works at the museum.

The balls are made out of recyclable material, so they won’t be wasted at the end of the summer. The museum is not exactly sure what it will do with the balls, but “they’ll have a good home,” Mustonen joked.

Besides being a fun place to spend a hot summer day, the indoor beach is also a learning opportunity. Filar said she hopes that seeing the converted Great Hall will make kids “start to think about ways that you can transform spaces through architecture and design.”

If you go

What: “The Beach”

Where: National Building Museum, 401 F Street NW.

When: Daily through September 7, 10 a.m. to 5 p.m.; until 9 p.m. on Wednesdays.

How much: Adults $16, kids $13.

For more information: A parent can visit nbm.org/exhibitions-collections/exhibitions/the-beach.html.

Sarah Polus