Once I went in, there were three things that really made a huge impression on me (these are the things I think about instead of listening to the Mass). First of all, the basilica is absolutely massive. According to the website, the upper church seats about 3,500 people, but can hold 6,000 people (I'm guessing thats the standing room capacity). It's one of the biggest churches in the world, and the largest in the US. The next thing I noticed was that the whole church is made of marble. Every color of marble imaginable. The floors have inlaid marble, the pillars are marble, the walls are marble. I can't even imaging how much just the marble alone must have cost, because this shrine wasn't completed until 1959. Then I started to look at the actual artwork. Everything is in mosaic. The ceilings are completely done in mosaic. Behind the altar there is an incredibly large portrait of a blond Jesus that is completely done in mosaic too. It's really quite awe inspiring.
All along the sides of the Upper Church there are small shrines to Mary (Well, this is the National Shrine of the Immaculate Conception.. I guess Mary is our national patron saint). Each shrine to Mary is from a different country. I'm guessing they are shrines to various Mary's that have appeared throughout history.. but don't quote me on that one.
There is also a downstairs to the basilica that was built first, I think around 1919 (I'm no historian, don't quote me on anything here), but the upper church wasn't completed until 1959. And even then, that was only just the structure, the artwork was completed at later dates. I guess the construction for the upper church was put on a hold until after the Great Depression and WWII. In the lower church, there is a large open space where the walls and pillars are lined with the names of families and organizations who donated money to the construction of the church. Beth's family was able to find a few family members on the walls there. In the lower church, there is also another "small" chapel where daily mass is held. I say "small" because it is bigger than quite a few churches I know of.
Anyway, I have a few pictures here, but I would check out http://www.nationalshrine.com/ to see more pictures and get more info about the history, and visiting. They do have tours, although I was not able to take one.