What's the must-see thing in Washington DC?

Most first-time visitors to Washington DC try to see everything on the National Mall in a single day. The Mall stretches 3.2 km from the Capitol steps to the Lincoln Memorial, and in mid-August the heat reaches around 32°C with humidity that makes the air feel wet on your skin. Trying to walk the full distance by noon is a recipe for the kind of headache the Smithsonian gift shops sell overpriced Advil for. The Lincoln Memorial is the one place worth building your day around. Go at dusk, around 8pm in August. The western exposure means the last sunlight hits the facade directly, and the Georgia marble shifts from bright white to warm sandstone. Inside the chamber, Daniel Chester French's 5.8-metre statue, carved from 28 blocks of that same marble, sits in a silence the open-air design somehow holds even with 30 people standing near you. The Gettysburg Address is carved into the south wall in letters you can read from across the room. The memorial opened in 1922 and draws roughly 6 million visitors a year, but the crowd thins quickly after sunset when the floodlights take over.

From the Lincoln Memorial, the walk east along the Reflecting Pool to the Washington Monument takes about 15 minutes at a comfortable pace. The obelisk stands 169 metres tall, started in 1848 and finished 36 years later. You can see a visible colour change in the stone about a third of the way up, where construction paused during the Civil War. Getting inside requires a timed-entry ticket from recreation.gov, and slots open at 10am the day before. They tend to go within the hour. If you miss one, the monument is almost as good from the grass below. The Smithsonian museums line both sides of the Mall from there, all free. The National Museum of Natural History, open since 1910, is the strongest first-timer pick among them. The Hope Diamond sits in a dim second-floor room, a 45.52-carat blue stone under glass that looks smaller than you'd expect. On a weekday morning the museum is quiet enough that you can hear the echo of your own footsteps in the rotunda.

The National Gallery of Art, on the Mall's north side at 4th Street NW, is the indoor pick most Washington DC visitors walk past. The West Building opened in 1937 with Andrew Mellon's private collection as its seed, and the European rooms are laid out chronologically. You walk from Giotto to Vermeer to Monet in about 90 minutes without backtracking. The Vermeer room tends to be cool and almost empty midweek. Stand in front of 'Girl with the Red Hat' for a minute. The brushwork on the hat is so loose it looks accidental, but the light on the face is precise. The East Building, connected by a dim underground walkway, holds modern and contemporary work, including a Calder mobile that moves with the building's air currents in the main atrium. Free, no reservation. The cascade-level cafe serves soup and sandwiches for $10-14, fair by Washington DC museum pricing.

The White House on Pennsylvania Avenue is worth seeing from the outside, but save the interior tour for a return trip. Access requires a request through your congressional representative weeks in advance, and the roped-off State Dining Room and East Room feel smaller than they look on television. The Pentagon, across the Potomac in Arlington, needs a reservation 14 to 90 days ahead and the tour is military-formal. Arlington National Cemetery, a 5-minute walk from the Arlington Cemetery Metro station, deserves a half day if you can spare it. The changing of the guard at the Tomb of the Unknown Soldier happens every 30 minutes from April through September and every 60 minutes from October through March. That silent, deliberate heel-click on stone carries across the plaza and stops every conversation around you.