Back when Billionaires’ Row was little more than Central Park South, the newly-converted historic Apthorp condominium building at 390 West End Avenue in the heart of the Upper West Side was said to be one of the city’s most expensive apartment buildings. Built for William Waldorf Astor in 1908, the building surrounds an interior courtyard, setting it apart from Manhattan’s many other regal residences. Converted to condominiums after being sold in 2006, the building’s most luxurious units arrived on the market in 2013, and new Manhattan sales records were set. The Apthorp may enjoy a moment in the headlines again: Its most expensive unit just hit the market asking $23.995 million. That number–or anything near it–will set a new record for residential units in the building. The larger of the two units in this combined sale is also the building’s largest renovated home, spanning a jaw-dropping 8,000 square feet.