DOWNTOWN DETROIT. Originally built with Ford money, this expansive, versatile complex is now the world headquarters of General Motors. Its multi-cylindrical design is the most distinctive aspect of Detroit's skyline, and the Ren Cen, as it's affectionately termed, houses offices, shops, banks, movie theaters, and restaurants. It's also convenient to the river and is the site of Detroit Marriott at the GM Renaissance Center and Courtyard by Marriott Detroit Downtown.