Imagine two photos of the Sydney Opera House, the awe-inspiring Australian landmark. Both show its distinct white roofs. Both show the beautiful blue waters that flow in front of this cultural destination. Both show a sailboat passing by, and both show the city's skyline just behind. So what's the difference between these two nearly identical photos? We'll never tell--the fun is in figuring it out!   Photo Fun Picture Puzzles: Cities features these and other photos from cities around the world. Each is paired with a photo that is almost its twin--except for one crucial difference. In the photos of brightly-colored buildings along a canal, is it the blue boat that's missing from the second photo? The gleaming white laundry hanging from the windows? The bird soaring through the sky? Readers will have to use all the powers of observation to find out.   With meters measuring the difficulty of each puzzle, boxes for readers to fill in their times and keep track of their progress, and--for those who just can't spot the difference--an answer key in the back of the book,Photo Fun PicturePuzzles: Cities is filled with the best brain-teasers for anyone looking for a fascinating challenge.