ACROSS THE STREET from the Central Park Zoo sits 834 Fifth Avenue, a limestone sanctuary of Manhattan’s elite for nearly a century. Almost from the moment its doors opened in 1931, the Art Decostyle masterpiece has been one of the city’s most prestigious addresses. Gaining access to 834 Fifth—home today to billionaires and Wall Street executives—is tough; the moneyed bastion has just 24 units. One is newly available following the death of Salomon Brothers legend John Gutfreund this past March. Even by New York standards, the property has an eye-watering asking price: $120 million.