North portal of Caltrain tunnel #1, looking down from the Mariposa Street bridge, San Francisco.

Shot with the Nikon D70s and the 18-70mm f/3.5-4.5 zoom at 70mm, ISO 400, f/4.5, shutter 1/50 sec. Cropping, exposure, contrast, saturation, levels, highlights,and color adjustments in Aperture.