As of mid-2004, the Department managed 507 million acres of surface land, or about one-fifth of the land in the United States. It manages 476 dams and 348 reservoirs through the Bureau of Reclamation, 388 national parks, monuments, seashore sites, etc. through the National Park Service, and 544 national wildlife refuges through the Fish and Wildlife Service. Energy projects on federally managed lands and offshore areas supply about 28 percent of the nation's energy production. Departments include:
Bureau of Indian Affairs
Bureau of Land Management
Bureau of Reclamation
Federal Executive Boards
Minerals Management Service
National Park Service
Office of Insular Affairs
Office of Surface Mining
United States Fish and Wildlife Service
United States Geological Survey
There is a museum inside the Department of the Interior
and it's free but you
will need to show a photo ID to get in and they probably
will put you through a metal detector and search you.
Monday through Friday: 8:30am to 4:30pm, except
for Federal holidays.
Saturday: Third Saturday of the month. 1:00pm to 4:00 pm Parking is available on the street (metered parking). It's free on weekends but you will need to keep checking the meter and putting more in occasionally. Hopefully you won't have to park far away. I suggest parking in an all day garage and metroing everywhere. It's expensive (25.00 sometimes for the all day parking and the metro is about a dollar or or two in and out one time).. However, it'll save you worry of finding a spot, fighting traffic, the risk of getting in an accident and a lot of time as traffic is heavy.
There is a gift shop and restrooms/water fountains. I do not know if there is a place to eat; there might not be, or it may be for employees only... so bank on eating before or after. No food or drink is allowed in the museum. You'll be walking a lot so wear good shoes.
Other than the museum, I don't know if you can just go in this building if you don't work there. They might let you into the lobby. What's notable about many of the government buildings in Washington DC is that many of them have beautiful architecture inside or artwork.