U.S. Supreme Court, 1 First Street NE
This was the site where the high court in 1896 ruled in Plessy v. Ferguson that racial segregation in public accommodations (such as railroads) was constitutional. Under this precedent, schools were segregated as well, and "separate but equal" became the standard doctrine until 1954.
This was also the site in 1954 where Thurgood Marshall successfully argued the landmark case Brown v. Board of Education of Topeka, resulting in a unanimous decision among the justices that "separate educational facilities are inherently unequal," overturning Plessy, and changing the policies of public schools across the nation.