The prominent Latin Rite Catholic basilica honors the Blessed Virgin Mary under her title of the Immaculate Conception as the Patroness of the United States. It is the tallest building in Washington, D.C. based on elevation, and houses 70 different chapels honoring the Virgin Mary and the cultures, people, and traditions behind the Roman Catholic faith. In addition to being the tallest building in D.C., the Basilica of the National Shrine is also the eighth largest religious structure anywhere in the world.

Pope Pius X himself personally contributed $400 to support the beginnings of the project back in 1913. Construction didn't start until seven years later in 1920 and the church opened - unfinished - in 1959.

It is estimated that one million pilgrims visit the basilica each year from around the world to admire the Neo-Byzantine architecture and mosaics. Another draw for the pilgrims is the collection of contemporary ecclesiastical art housed inside of the Basilica; it is the largest such collection on earth.

The church is often confused with the Washington National Cathedral, another prominent church in the Washington, D.C., area. The National Cathedral, though, is an Episcopal church chartered by Congress years ago as the National House of Prayer.

Obscura Day location: April 9, 2011.