The Woolworth Building penthouse is on the market for $79 million.
The five-story “castle on top of a castle” — as developer Ken Horn calls it — starts at 727 feet up.
The lower Manhattan terracotta and limestone building, designed by Cass Gilbert, was the world’s tallest building from 1913 to 1930.
Thirty-two condos start on the 29th floor, collectively known as the Woolworth Tower Residences.
Details include 125 windows, 24-foot ceilings, a private elevator — and a 408-square-foot observatory terrace. The buyer will also have access to the building’s amenities, which include a gym, a lounge, a pool, a wine cellar and tasting room.