In the city within a city rising west of Pennsylvania Station are many astonishing sights.

The most astonishing — for the moment, anyway — is a mammoth steel structure, as long as a city block, that seems to float 51½ feet over the ground at Ninth Avenue and 33rd Street.

With a volume of 1.2 million cubic feet, this structure alone would be more than enough of a building in most parts of New York City. But on the Far West Side of Manhattan, which is being redeveloped at a gargantuan scale, it is merely a pedestal for a skyscraper that will eventually soar 995 feet.

The $1 billion skyscraper, called 1 Manhattan West, will not simply sit on this pedestal. It will balance on it.