Chicago Architecture Center, daytime, sunny weather, Willis Tower (Sears Tower), glass and steel skyscraper, modern architectural style, reflective windows, bustling city streets, tourists walking, guided tour group, professional photographer capturing cityscape, Canon EOS camera, 24-70mm lens, F/2.8 aperture, low-angle shot, wide-angle composition, vibrant blue sky with puffy white clouds, dramatic light and shadow, urban landscape, people in motion, blurred background, high-rise buildings, city life, American flag waving on rooftop.