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Photo: NPS/Catie Drew, Public domain via Wikimedia Commons
On Columbia Island, along the Mount Vernon Trail
The Navy and Marine Memorial, is a monument honoring sailors of the United States Navy, Coast Guard, the United States Merchant Marine, the NOAA Commissioned Officer Corps and others who died at sea during World War I and other times. It is located in the George Washington Memorial Parkway in Lady Bird Johnson Park on Columbia Island in Washington, D.C.
© OpenStreetMap contributors
While lingering is not recommended for security reasons, you should know it is the largest office building in the world, and covers 4 zip codes. (Army, Navy, Air Force and Department of Defense). Tours are available by online reservation made 14-90 days in advance. The Pentagon Memorial is open 24 hours to visitors on the Washington Blvd side, where Flight 77 hit. Photography is allowed at the memorial, but is not permitted anywhere else on the Pentagon grounds— take photos anywhere else on site, and you may face a lengthy interrogation by the Pentagon Police and will probably be asked to delete the images. On a lighter note, the interior courtyard is irreverently referred to by employees as "Ground Zero," as it was the target of a number of Soviet missiles during the Cold War. There is no public parking at the Pentagon but it is about a 5-minute walk from the Pentagon City Mall through a tunnel.
Just outside the Pentagon, and accessible to visitors
A historic bridge built in 1932 providing a line-of-sight between Arlington House and the Lincoln Memorial, symbolizing the rapprochement between the North and South after the Civil War
Honors the Naval Construction Battalions, with panels depicting their missions since 1942.
Contains information about the cemetery and the tomb of the unknown solder. There is also a large parking garage which can be a good place to dump your car before catching the subway into D.C.