Costing an estimated $25 billion, Manhattan's Hudson Yards neighborhood is already the largest real-estate development in American history.

And soon, the neighborhood will break another record. 30 Hudson Yards, a skyscraper under construction on the island's far west side, will feature the highest outdoor observation deck in New York City and the Western Hemisphere.

A construction crew began installing the 765,000-pound, steel deck on Tuesday. When complete, it will jut out from the tower 1,100 feet in the air.

Take a look below.