"As prices continue to decline in the luxury market, developers are keen on maximizing every square foot, including below-grade space, while buyers seek out bargains in a supply-heavy market," reported Stefanos Chen for The New York Times.
One buyer told Chen she bought a 2,100-square-foot, two-bedroom underground duplex on the Upper West Side for $2.3 million — twice the size of her place in Williamsburg, Brooklyn. The smaller apartment above her was listed for roughly $1 million more, she said.