Last weekend, the National Building Museum in Washington, D.C., opened a 10,000 square-foot ball pit to the general public, and everyone cheered that, finally, someone made their childhood dreams come true.

The National September 11 Memorial & Museum (branded as 9/11 Memorial and 9/11 Memorial Museum) is the principal memorial and museum commemorating the September 11 attacks of 2001, which killed nearly 3,000 people, and the World Trade Center bombing of 1993, which killed six. The memorial is located at the World Trade Center site, on the former location of the Twin Towers, which were destroyed during the attacks. The World Trade Center Memorial Foundation was renamed the National September 11 Memorial & Museum at the World Trade Center in 2007.

The delegates arrive at the Great Hall of the People before a plenary session of the National People's Congress on March 11, 2011 in Beijing, China. The NPC will take place until March 14. (Photo by Feng Li/Getty Images)

This Sunday, September 7, 2014 photo provided by Rachel Kirk shows smoke from a fire rising above Little Yosemite Valley near Yosemite National Park, Calif. (Photo by Rachel Kirk/AP Photo)

Miss California Crystal Lee performs during the Miss America 2014 pageant, Sunday, September 15, 2013, in Atlantic City, N.J. (Photo by Mel Evans/AP Photo)

Taylor Swift performs “All Too Well” at the 56th annual Grammy Awards at Staples Center. (Photo by Matt Sayles/Invision)

Runners cross the Verrazano-Narrows Bridge shortly after the start of the New York City Marathon in New York, November 2, 2014. (Photo by Lucas Jackson/Reuters)

Actress Zendaya arrives at the 27th Annual Kids' Choice Awards in Los Angeles, California March 29, 2014. (Photo by Danny Moloshok/Reuters)