Metropolitan was the name of a building on Fifth Avenue, in New York City. This building, described as a "...gray old beaux...", along with the Union League and the New York Yacht, was a museum. This was a gathering place for wealthy New Yorkers in the early 20th century.
In The Big Good-Bye, this was one of the attractions on this avenue that drew the attention of the master criminal Silent Forrester as he was being chauffeured to the hotel Plaza. (TNG: "The Big Goodbye")