Post your guesses in the comments section below.
Guess correctly and be crowned "San Lorenzo know-it-all" for the week.
Congratulations to Larry Kinslow for being the first to correctly guess . The building is home of Insta-Smog at 254 Sycamore St. A special thank you to Keith Barros who submitted the photo to us.
Have your own photos around town that you'd like featured in Castro Valley Patch's photo challenge? Send them to email@example.com and see if you can stump our readers!