https://en.wikipedia.org/wiki/Librarian_of_Congress

If I may go into fanboy mode for a moment, I'd like to say that in my opinion the Library itself is one of the crown jewels of the federal government. It is also definitely worth a visit if you're ever in DC. They give free tours of the Jefferson building, and besides the beautiful architecture of the building itself, there are some very interesting exhibits on display. There's a surprising amount to see, and the staff are great- very knowledgable and friendly.

Besides its main missions of supporting congressional research and acting as the central repository library, the LoC also does a ton of great research on media preservation and archival practices... I got to tour one of their labs once- in one room I talked with an expert in the chemistry of inks used in the 18th and 19th centuries, and in the next room heard from other people who specialized in CD and audiotape manufacturing, who could talk about how specific manufacturing plants in Japan changed processes from year to year and how that affected the archival lifetime of their products. Just amazing stuff, and that wasn't even scratching the surface.