Abutment wing of the south portal of Caltrain tunnel #1, near the 22nd Street station, San Francisco.

Shot with the Nikon D70s and the 18-70mm f/3.5-4.5 zoom at 46mm, ISO 400, f/4.5, shutter 1/60 sec. Exposure, contrast, saturation, highlights, and levels adjustments in Aperture.