From the Pilgrim Observation Gallery of the Gothic building you can view all the landmark monuments on the Mall, the White House, the Capitol and Pennsylvania Avenue. A sunny day is the best time to see the great melding of 19th and 20th century architecture of the city from the 50th-floor Skywalk. The Hancock Tower appears like a hanging mirror in contrast to the heavy stone buildings around it. And you can see the street grid of Back Bay, the Charles River and Cambridge. On clear days, you can even spot Cape Cod.
Evening is the best time to go, when the stainless steel arch is ethereal by moonlight.