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.

Greg Carr says he knew he had to buy the penthouse at 170 Fifth Ave. when it first came up for sale in 2001. The midrise prewar building had been converted into condos for the first time, and he liked the downtown location across from the Flatiron Building.