By day or night the National Mall is worth a visit! Flanked by the US Capitol and the Washington Monument, the Mall is lined with Smithsonian Museums (National Museum of Natural History, National Museum of American History, Air and Space Museum, Hirshhorn Museum and Sculpture Garden, National Museum of African American History and Culture, and many more) and the National Gallery of Art, which are all free and open daily from 10 am - 5:30 pm. The grounds are a beautiful outdoor walk, and walking west will take you to important national monuments such as the Lincoln Memorial and reflecting pool, World War II Memorial, Vietnam Memorial, and those at the Tidal Basin (Jefferson Memorial and FDR).