Here are the typical features: Office and/or residential tower(s), atrium, underground parking, enclosed shopping and circulation. Examples include Water Tower Place in Chicago, World Trade Center in NYC, IDS Center in Minneapolis, Renaissance Center in Detroit.
Do you know if any such downtown megaprojects from the 1960s through the 1980s have been substantially renovated or altered in recent years? I know that GM is making substantial changes to Detroit's Ren Cen. Any others?