Chicago architect Lucien Lagrange said the conversion must preserve the building's old-world façade while converting the interior of the 259,700-sf structure to one-, two- and three-bedroom apartments. Lagrange, whose high-end condo conversions have included 65 E. Goethe St. and 840 N. Lake Shore Dr., said a "pretty deep" basement allows for sufficient parking for the future condo owners.

Built in 1910, the hotel's guestbook included several U.S. presidents, including Franklin D. Roosevelt and John F. Kennedy. "Major decisions have been made in that hotel," Lagrange said. The Maharishi Mahesh Yogi, whose organization owns the hotel, had to make one himself concerning the Blackstone. After buying it in 1995 with intentions to renovate it as a hotel, the Maharishi Global Development Fund reportedly received multiple offers starting at $20 million before deciding to convert it to condos. The hotel closed in November, when room rates were about $105 a night.