731 Lexington Avenue / One Beacon Court

This $630 million mixed-use development was built on the site of a long-defunct Alexander's Department Store and opened in 2005. The design by Cesar Pelli & Associates is actually two separate towers: a 10-story building on Third Avenue and an 815-foot glass curtain wall tower on Lexington. The first 30 floors of the tower are steel frame construction for office space, dominated by the financial information services company Bloomberg LP. The upper 23 stories of the tower are reinforced concrete containing 105 luxury condominiums. The first three floors including street level contain around 160,000 square feet of retail space. (reference)

One notable hidden feature of the design is a tuned mass damper consisting of 650 tons of concrete block at the top of the building that shift the building's weight to counter motion caused by wind.

The most notable visible highlights of this otherwise ordinary structure are the crown of the tower which glows white in the dark and an oval-shaped public plaza between the two buildings which is illuminated with colored lighting and is especially stunning at night.