Apartments go on the market every day in New York City, but there are some real estate gems that don’t come along very often. A residence in a Beaux Arts townhouse designed by Carrère & Hastings (1895‒1924) is one such rarity. So, when Sandra Nunnerley became aware of two apartments in an Upper East Side building by the legendary New York firm, she knew it was an opportunity she couldn’t pass up.