O.Henry and H.G.Wells wrote about it:Flatiron

In his short story "Lost on Dress Parade"  American writer O. Henry  wrote: "... He was employed in the  office of an architect. He was twenty-two years old; he considered  architecture to be truly an art; and he honestly believed--though he would not have dared to admit it in New York--that the Flatiron   Building was inferior to design to the great cathedral in Milan. "

I visited  the  great cathedral in Milan and I disagree with  the architect,  but still Flatiron Building,   at 175 Fifth Avenue, is one of the most famous building is New York. It  sits on a triangular block formed by Fifth Avenue, Broadway and East 22nd Street. The building, designed by Chicago architect Daniel Burnham and built in 1902, allowed it to fill the  wedge-shaped property.

Upon completion , it was one of the tallest buildings in the city.  Upon  the completion of the there were a lot of negative reviews in the newspapers:  The New York Tribune called the new building "A stingy piece of pie ... the greatest inanimate troublemaker in New York", The New York Times called it a "monstrosity".
But public was more enthusiastic.    Futurist English writer  H. G. Wells wrote in his 1906 travel  essay "The Future in America: A Search After Realities" :  " I found myself agape, admiring a sky-scraper the prow of the Flat-iron Building, to be particular, ploughing up through the traffic of Broadway and Fifth Avenue in the afternoon light. The New York sundown and twilight seemed to me quite glorious things".

Flatiron  was originally called the Fuller Building, after the Chicago-based George A. Fuller Company, which built and developed the building. The triangular lot bounded by Broadway, Fifth Avenue and 22nd and 23rd Streets had been called the “Flat Iron”' for years prior to the building's construction, and some of the few early drawings of the building that exist already used the name “Flatiron".

 When constructed  the building rose 20 stories. The  21st floor   was added in 1905.  The 21st floor originally housed a restaurant and an observation, but both of these were closed down many years ago. The building’s bathrooms are apportioned such that the men’s rooms on even floors and the women's rooms on odd ones.
The thinness of the building (it was called the most slender building in New York), with all three façades facing streets, enables many employees there to enjoy well-lit office space.
Because of the shape of the building, winds swirl around it. 

During the early 1900s, groups of men would allegedly gather to watch women walking by have their skirts blown up, revealing legs, which were seldom seen publicly at that time.   In 1905 Crescent Films made a  movie  entitled  " The Flatiron Building on a Windy Day", that “gives one a general idea of what women experience on a windy day around this noted corner,” according to a film catalog of the day.

Edward Steichen. 1905.
Photo of Flatiron Building

San Francisko
Flatiron building

The Flatiron   attracted the attention of numerous artists.  A lot of photographers took the Flatiron as the subject of their work.  As an icon of New York City, the Flatiron Building is a popular spot for tourist photographs, making it "possibly one of the most photographed buildings in the world".

San Francisco has its own California's Flatiron Building, constructed in the Financial District in 1913. Atlanta has its own Flatiron building constructed  in 1897, five years earlier that Flatiron in New York.

In December 2013  the Museum of Mathematics (MoMath) and about 500 math enthusiasts of all ages proved that   building is approximately in the shape of a very special type of right triangle. People lined up around the three sides of the building holding  light sticks   end to end. By counting  the sticks MoMath was able to estimate the length of the building's sides in terms of lights ticks. So the results were:   75, 180 and  195  light sticks- Pythagorean triple. I wrote about this event in one of my posts.