The Library of the Department of the Interior (DOI) was established in 1850 by Thomas Ewing, Jr., the son of the first Secretary of the Interior. The library today is housed in the Department of the Interior building on 18th and C street. The DOI consists of several bureaus: National Park Service, U.S. Fish and Wildlife, Bureau of Indian Affairs, Bureau of Land Management, Office of Surface Mining, Bureau of Ocean Energy Management, Bureau of Safety and Environmental Enforcement, U.S. Geological Survey, and the Bureau of Reclamation. As such, the library collection contains a wide variety of information to match the varied areas of interests of DOI affiliates. More information about DOI library collections can be found here. The library provides access to an extensive amount publicly accessible information on the web through it's Internet Guides. The Library website is definately worth checking out, as well as browsing through to other areas of the DOI website as a whole. The DOI itself has a presence on various social media networks, and provides a variety of multi-media resources such as Webcams, Videos, and Podcasts.
The library is also an architecturally fascinating space. You can read about the Art and Architecture on the website and the library is open to the public if you are located nearby and would like to stop and visit. The Park Ranger Speaker Series is a great way to learn more about aspects of sites of interest or history of Washington, DC.
You can also see the library in film, such as in the 1987 Kevin Costner thriller No Way Out. The library's spectacular stacks can be seen during a chase scene near the end of the movie. The Stacks consist of six decks on three floors, constructed by Navy contractors. The stairs between the decks are a steep an narrow climb, and navigating the space is an impressive, although slightly claustrophobic experience.
I recently took some pictures from one of the rare book section balconies. If you do happen to visit, be sure to ask the reference librarian about the clock.