This is the Tomb of the Unknown Soldier at Arlington National Cemetery. I have been to Arlington National several times to visit JFK's grave and my uncle's and it always reminds me of the sacrifices others have made for this country.
If you ever have a chance, then you need to go and watch the changing of the guard. It is a very solemn occasion.
It is also necessary to visit the Viet Nam Memorial (Wall), the Koren War Memorial (Korean War) and the World War 11 Memorial (WW11).
Finally.....we must never forget our MIA until they are all returned to their families.