The Metropolitan Branch Trail, a rail-trail conversion that was originally conceived of in 1988, will eventually be an 8-mile trail running from DC's Union Station up to Silver Spring, Maryland. The existing portion of the trail connects a number of vibrant neighborhoods, and boasts a number of great views of places in the city as well as some unique artwork.
It's pretty easy to see DC's arguably most famous dome--the U.S. Capitol, of course--headed southbound on this trail. But find this cache and you'll be treated to a direct view of another very famous dome, which is more hidden by the buildings along the trail.
The National Shrine of the Immaculate Conception is an important landmark in DC, located on Michigan Avenue, in the neighborhood of Brookland at Catholic University. It is the largest Catholic church in the United States, and also the 21st largest church building in the world. Construction began in 1920, and the church was opened in 1959, though construction continued until 1961. Though a fairly recent structure, the project was originally thought up by Bishop Thomas Joseph Shahan, who put $400 of his own money into the idea back in 1914.
Coordinates are as close as possible--please replace it just like you found it. Watch out for lots of muggles, especially during AM/PM rush hour (there is a day care next door). Remember to bring a writing utensil!
Congrats to wizardofmd69 for FTF!