A lighted glass walkway radiates the mezzanine level and encircles the base of cylindrical hotel tower for ease of navigation. This ringed glass walkway is about wide and has a circumference of approximately or about one-eighth of a mile around. The ringed walkway's diameter is approximately . It links to several other walkways in the complex. The five-story Wintergarden atrium leads into the central area which has an eight-story atrium lobby with rounded concrete balconies and terraces. The Highlands is located on Floors 71 through 73, which includes a restaurant, scotch bar, and special events space. The hotel has no floors labeled 7, 8, or 13. The hotel features a major conference center with of meeting space including a Renaissance Ballroom for up to 2,200 guests with for events, one of the largest in the United States. John Portman designed the five-building rosette with interior spaces. In 1977, its central tower opened as the tallest hotel in the world. It remains the tallest all hotel skyscraper in the Western Hemisphere. The smaller cylinders on sides of all the towers house the elevators. The four surrounding 39-story office towers (100–400) each reach 522 feet (159 m) and have a total of of space. Each 39-story tower has a base five-story podium structure with for retail space for a total of . A portion of the central atrium area houses GM World, a showcase for GM vehicles. Two 21-story towers (500–600), designed by Portman and constructed in 1981, reach 339 feet (103 m). GM gained control of Towers 500 and 600 in 2001. Tower 500 has of office space and an additional of retail space. Tower 600 has of office space and an additional of retail space. Towers 100 and 200 front Jefferson Avenue. Towers 300 and 400 are on the main Wintergarden/Atwater Street entrance facing the Riverfront. The GM Renaissance Conference Center is located on the second floor of tower 300. In December 2001, the General Motors unveiled the Wintergarden retail atrium. Designed by Skidmore, Owings & Merrill, it rises tall at its highest point opening direct access to the International Riverfront. In addition, the atrium contains of retail space and of contiguous main floor exhibit space which was used by the media during Super Bowl XL. The design is consistent with the themes of Brutalist architecture, especially in the heavy massing of concrete on the lower floors, but the 2001