Amazing to me that Washington National Cathedral was "just" completed in 1990. The first stone was laid in 1907. Plans for such an institution, a "church intended for national purposes," had existed since 1792. The original intended space is now occupied by the National Portrait Gallery. The current location (Wisconsin and Massachusetts Aves NW) makes the Cathedral one of the the District's most recognized buildings; you can see it atop Mount Alban from so many parts of Washington and even Virginia (especially as you approach via 395). At 700 feet above sea level, the tops of the two towers are the highest spots in the District. The Cathedral is also the 6th largest in the world. It's a place for all worshipers, but everything inside is Christian related and it is an Episcopal Church.
I visited over the holiday break to see the earthquake damage up close. It is extensive, but the interior was largely untouched. I was happy to see the amazing stained glass windows intact -- there are over 200. There is even an exhibit about the earthquake's impact on the first floor. There's so much to see here, I highly recommend a trip. And make sure you get up to the 7th floor of the towers for unparalleled views of the District, Maryland and Virginia. You can even see the Blue Ridge Mountains! They ask for a small donation, but it's worth the hour+ you'll spend exploring. There's not really a Metro station nearby (Tenleytown at 1.5 miles), but the 30s buses, the 96 bus and the X3 bus drop off adjacent to the Cathedral. If you're up for it, the mostly uphill walk from Woodley Park Metro is beautiful.