Almost everything on the Mall is free, but the good rooms are now rationed by timed-entry passes worth booking thirty days out, while the memorials need no ticket at all.
National Air and Space Museum
At 650 Jefferson Drive SW, open 10am to 5.30pm daily and closed 25 December. Free, but you need a free timed-entry pass; inside are the 1903 Wright Flyer, the Apollo 11 command module Columbia and Mercury Friendship 7, plus a planetarium and an IMAX screen.
National Museum of African American History and Culture
At 1400 Constitution Avenue NW, open noon to 5.30pm Monday and 10am to 5.30pm Tuesday to Sunday, last entry 4pm. Every visitor of any age needs a free timed-entry pass: advance passes are released thirty days ahead on a rolling basis, and same-day passes go online by 8.15am. Weekends and holidays are the busiest.
Library of Congress, Thomas Jefferson Building
At 10 First Street SE, open Tuesday to Saturday 10am to 5pm with last entry at 4.30pm, plus Thursday evenings 5–8pm for Live! at the Library. A free timed-entry ticket is required, bookable thirty days ahead or same-day from 9am. Free five-minute walkthroughs of the Main Reading Room run Tuesday to Friday 10.30–11.30am and 2–3pm and Thursday 5–7pm, first come first served from the Great Hall.
National Gallery of Art
Admission is always free and, unusually for the Mall now, needs no pass or ticket at all. Open daily 10am to 5pm, closed 25 December and 1 January: the West Building at 6th and Constitution NW holds the older collection, the East Building at 4th the modern and contemporary, and the six-acre Sculpture Garden sits at 7th.
Lincoln Memorial and the Reflecting Pool
At 1100 Ohio Drive SW; the chamber and exterior are free and open to the public with no booking, which makes the walk along the Reflecting Pool the easiest thing to do in the city after a day of timed entries. Tickets are only needed for the separate Undercroft tour.