Despite its dense forest of giant towers, San Francisco at street level receives a surprising amount of sun at this time of year.  The high sun floods the streets with light from overhead, so for much of the day, the towers don't keep the sun from directly lighting, and heating, the streets and sidewalks. As a result, vividly blue sky is a highly -- so to speak -- visible component of the scene viewed from street level.  Here are some examples.  

Please note that the modern buildings have the strongest geometrical values in a graphic sense.  Nonetheless, I am including an early pioneer of SF skyscraper construction, the Hobart Building.  And also an example of new construction: the Salesforce Tower, that will be the tallest building here when it is finished.  Whether its aesthetics will be up to the standard is yet to become apparent.  Its photograph here nestles it in with other tall buildings, so it doesn't seem out of place.  But viewed from a distance (say, from the Legion of Honor), it is remarkably taller than the other visible towers.  And assuming the Golden Gate isn't a "building" as such, it is nonetheless simultaneously a structure and an example of high structure in both the vertical and stylistic sense.