Begin at the Basilica of the National Shrine of the Immaculate Conception (400 Michigan Avenue, NE). This is the largest Roman Catholic church in North America and one of the ten largest churches in the world.  Inside, you’ll find a diverse array of chapels dedicated to cultures from around the world, as well as the largest collection of contemporary ecclesiastical art on earth. You’ll walk the same steps of prominent visitors Pope Benedict XVI, Pope John Paul II, and Mother Teresa. To reach the Basilica, take the Metro to the Brookland-CUA station on the red line and walk three blocks.

Grab some lunch in the Basilica’s cafeteria, and then take a stroll through the campus of neighboring Catholic University.
 
Next, walk to the Franciscan Monastery (1400 Quincy Avenue, NE) which is about ten blocks away. The Monastery features replicas of Holy Land Shrines and 40 acres of gardens, allowing for a peaceful escape from the bustle of the city. Enjoy gardens that feature overflowing rose beds and other ornamental plants and trees.

Other suggested religious stops outside of Northeast:
Washington National Cathedral
America’s Islamic Heritage Museum
Jewish Historical Society of Greater Washington