Part of NBC's space also extends into the central part of the tower. Since the middle of a block was seen as typically not a well-desired location for Manhattan office space, this segment was planned without windows, which was suitable for NBC's studios. This section of the building contains a "Garden of the Nations" atop its roof. In 1936, the central section's roof temporarily housed a prototype of an apartment, which was used to advertise the Rockefeller Apartments between 54th and 55th Streets. Afterward, the roof was proposed as the site of a solar heat-powered "management and conference center".