The Basilica is one of the most visited church in Washington DC area due to its renowned beautiful sacred art and unique architecture. It is considered to be the patronal church of US catholics and America's preeminent Marian Shrine. It is also the largest Roman Catholic church in the US and in North America, and one of the 10th largest churches in the world.
In 1913, the Catholic University of America suggested building a national shrine in honor of the Virgin Mary, wherein the archbishop of Baltimore laid the foundation stones on September 23, 1920 after the building designs were completed by the two architects, - Maginnis and Walsh of Boston who were then the chosen ones as the architects of the shrine. The construction stopped when the bishop died in 1932. It was during the year 1953-54 (Marian Year) that the American Catholic Bishops started to lead a fund raising effort. It was then dedicated on November 20, 1959 as a National Shrine and was elevated as a minor basilica by Pope John Paul II on October 12, 1990.
There are numerous chapels, statues, shrines etc.that are to be seen both at the Upper Church and at the Crypt level.
Guided tours are conducted daily including group tours as well. Audio tours are also available if you prefer it more convenient. All tours are free. :)