In the big, ongoing festival of American culture, the National Mall in Washington is the main stage. Ever since the Smithsonian Institution erected its imposing stone castle there in 1855, the linear park has been assembling an all-star lineup of museums and monuments that collectively tell our nation's story. The mall has even managed to find room for events that happened abroad, like the Holocaust. And yet, a fundamental part of the American story, one that informs almost everything that happens in our country, has largely been left out of the mix.

That omission will finally be rectified Sept. 24, when the National Museum of African American History and Culture opens its new home overlooking the Washington Monument. Designed by Tanzanian-born superstar David Adjaye and Central High grad Philip Freelon - two of a tiny contingent of black architects working in the U.S. - the stunningly radiant building is unlike anything else on the mall, or, for that matter, anything else in official Washington.

Of all the civic buildings that dot the park and its environs, the museum is the only one not weighed down by a quarry's worth of stone, most of it white. Instead, in a refreshing break from tradition, the architects have fashioned the African American museum out of glass and wrapped it in a lacy metal scrim the color of dark honey. The scrim rises in three angled tiers that suggest both a traditional African crown and America's celebrated waves of amber grain.

The choice of the building's skin color, and the symbolism embedded in the design, are obviously intended to make a strong statement about race. In its architecture and its exhibits, the museum fuses black history with American history, something it does with masterful nuance.

Even while the museum was still under construction, one of the most popular spots to photograph the building was from the corner of 14th Street, where the crown - or, as the architects call it, the corona - sharply contrasts with the Washington Monument's white stone and classical form. The angle of the obelisk's crowning pyramid is 17.5 degrees, the precise tilt of the corona's tiers.

George Washington is honored for being the father of our democracy, yet he was also a slave owner. Placing these two structures in tandem on the National Mall drives home the disconnect between the country's lofty goal of creating freedom for all and its reality.

The corona was originally supposed to be bronze, but the metal proved too heavy, and the architects switched to coated aluminum. The material has a gossamer lightness; the corona seems ready to levitate. Its upward slant conveys a feeling of uplift, which is also a major objective of the exhibits. At several places, the scrim opens up to frame strategic views of the mall.

Yet the metal screen also conceals, and you can't help think about how blacks in America have been invisible for so long. The opening of the museum comes at a charged moment in our national life, when institutionalized racism is being exposed by internet videos of police brutality. Though the museum is an old-school, analog institution, it, too, promises to peel back our hidden history.

The greatness of the mall lies in the symbolic juxtapositions of its monuments. The African American museum is situated midway between the U.S. Capitol, erected with slave labor, and the memorial to Lincoln, who freed the slaves. It stands next to the American History Museum and down the street from the White House. The place still resonates with memories of civil rights marches. The museum sits above the buried Tiber Creek, which was used to ferry enslaved Africans to Georgetown.

There was initially some grumbling about making room on the mall for the project. Several U.S. representatives complained it would open the floodgates to museums honoring other ethnic groups. While America became what it is because of its extraordinary mix of people, what that view overlooks is the degree to which the African American story is inseparable from the American story.

Museum director Lonnie G. Bunch III was ultimately able to persuade the holdouts that "you can't understand American notions of freedom without including American notions of slavery." In 2003, President George W. Bush authorized the museum. It took 13 years to raise the $540 million for the project. Half came from private donors, including $21 million from Oprah Winfrey, whose name appears on the museum theater.

Most visitors will enter the museum from the mall side. In a reenactment of the forced Atlantic migration, they will cross a bridge over a flat fountain before reaching the shelter of the museum's extended entry porch.

The procession through the museum will remind many of the experience at the influential U.S. Holocaust Memorial Museum. That's because the exhibit designers are the same, Ralph Appelbaum Associates. His firm has perfected a storytelling style that now dominates America's history museums.

Because of Washington's height limit, Adjaye and Freelon were forced to put half of the 400,000-square-foot building underground. Although the lack of natural light sounds unappealing, the designers use the condition to their advantage. The exhibits start at the lowest point and move up in roughly chronological order.

Though it's possible to go directly to a specific gallery, the museum makes the most sense starting at the beginning, with the accounts of arrival and enslavement. As visitors make their way through the exhibits - including an actual slave cabin, segregated train car, and plane flown by Tuskegee Airmen - they are literally climbing out of slavery.

By the time they reach the sections devoted to the post-emancipation triumphs of music, literature, and sports and to civil rights, visitors are at street level. Light floods into the corridors. Several Philadelphia figures get prime treatment in those upper galleries, including the milliner Mae Reeves, musicians Kenneth Gamble and Leon Huff, and Hercules, Washington's enslaved chef.

If there is a downside to the way the exhibits are arranged, it is that the sheer volume of material devoted to overcoming adversity can overwhelm the outrage of the slave period and segregation. This is a righteous museum, but not an angry one. As the feminist writer Bell Hooks says in one of the rotating inscriptions, "Oppressed people resist by defining their reality." This is the reality that the African American museum chose for its place on the National Mall.