The National Museum of Natural History has become the steward of one of the largest natural history collections, with over 126 million specimens including hundreds of mammals from Africa, Australia, and the Americas. This museum always tops visitors' lists for its vast collection and the famous Hope Diamond. While the museum is free, some exhibits and the IMAX theater require admission.
This museum is always busy, but more so on holidays and weekends. It's best enjoyed early in the day and during the week, if you can.