Smithsonian National Museum of Natural History
My favorite display was the deep sea creatures. There's a giant squid, which I found pretty interesting. I also highly enjoyed the film about a group of scientists that get to explore the sea floor. As a matter of fact, my daughter even sat still to watch this one! That is a feat in itself.
Usually, I have a difficult time recommending museums to people who aren't the nerdy type. However, I truly feel this is a museum that everyone can enjoy. Between the butterfly enclosure, the gemstone collection, the live insects, and the history of the creatures of the earth...I'm sure everyone can find at least one thing they'll love. I know it was true in our group!