From the day it opened in 1984, the distinctive 57-story granite building at 950 N. Michigan Ave. has been known as One Mag Mile simply because it is at the inside corner of Chicago’s Gold Coast – where Lake Shore Drive turns east and the city’s world-class shopping and hotel district – The Magnificent Mile – begins. Its unique design faces Oak Street Beach. Designed by Skidmore, Owings and Merrill,…