It's not far at all. You can get to the Capitol (The end of the Mall) in probably mess than a quarter of a mile from Union Station.
The distance between New York Penn Station and New York Union Square is walkable. The total distance on foot is 1.65 miles
The distance from Brookfield Illinois, home of the Brookfield Zoo, to Chicago is 12 miles. This is the distance from Union Station to the Brookfield Prairie Street train station.
Easy. Just walk towards the Capitol Building, you can see it when you leave the station. Once in front of the Capitol, turn right and walk along the Mall to the National Gallery, which will be on the right side of the Mall.
Assuming you're in DC, that's 5 miles.
You can get from Dulles to Union Station by air. The average flight time is 49 minutes and the flight distance is 281 miles or 452 km.
Union Station opened on October 27, 1907
Union Bridge Station was created in 1902.
Charlottesville Union Station was created in 1885.
Durand Union Station was created in 1903.
Memphis Union Station was created in 1912.
Hartford Union Station was created in 1889.