Visitors to New York City’s famed Flatiron Building may have noticed the landmark’s lesser-known neighbor — a narrow high-rise that would be modest if not for its extravagant gold dome. Now, the 5,777-square-foot penthouse that occupies the shimmering dome (and the two-story octagonal cupola it crowns) is on sale for $25 million.

A gem of an aerie at 170 Fifth Ave. has a dazzling amenity that's rare to find in New York -- and now a new generation stands to get it.