Yesterday, Hudson Yards revealed plans for Thomas Heatherwick’s $150m Vessel, a vertical public space akin to the city’s wildly popular High Line that now anchors the West Side.

It’s hard to classify this kind of structure. Vanity Fair’s architecture writer, Paul Goldberger, says it was one of the city’s best kept secrets until yesterday:

Heatherwick has figured out how to combine the showmanship of a Ferris wheel with the architectural power of a monumental staircase. I suspect people will want to start climbing up it the minute they see it. There are 2,500 steps, and the latticework design means that there are an almost infinite number of routes you can take up and across and around and through it as you climb. When it is filled with people it will look like a giant beehive.

Related Companies, the real-estate behemoth behind Hudson Yards, is calling it an “urban landmark” for the time being, which I suppose is better than thinking of it as the world’s largest Stairmaster. Stephen Ross, the 76-year-old chairman of Related, clearly wanted something more than just an opportunity for public fitness. Like most big-time developers, he has a serious case of Rockefeller Center envy: he wants his project to be its 21st-century equivalent. Ross was perceptive to see that the brilliance of Rockefeller Center’s design was not only in its architecture but also in its public space, that combination of Paul Manship’s great Prometheus statue and the ice-skating rink. Hudson Yards, too, is getting a public square, a five-acre landscape designed by Thomas Woltz, but Ross wanted it to be punctuated by something more than sculpture. He asked several designers for proposals, and was smitten with Heatherwick’s idea and with the notion that it could become a symbol not only of the Hudson Yards project, but also of the city itself.

The Mystery of Thomas Heatherwick’s Top-Secret Hudson Yards Project  (Vanity Fair)