A museum, part of the Smithsonian Institution, located in Washington, D.C.. Not to be confused with The American Museum of Natural History, which is in New York City. In short, it's the dinosaur museum of the Smithsonian. It's got fossils of stegosaurus and Tyrannosaurus rex and all that cool stuff. They recently renovated their gem exhibit, and it's a real gem! Ahem. Sorry about that. Seriously, the gem exhibit is very well done. It's got just about every type of stone you could think of, plus the infamous Hope Diamond. It's insect zoo has also been recently renovated, so it's fun to go if you like to look at cockroaches and other good stuff like that. Has a fairly extensive collection of stuffed animals that are native to the region -- so lots of rodents and birds. Various other exhibits are there as well: non-European cultures, ecology, and miscellaneous temporary exhibits. There's also a new IMAX theater, which is always fun.
If you walk into the museum from the mall, you see a big stuffed elephant up on a pedestal, looking at you. Very cool.