Take a look — a close look — at the world’s most beautiful cityscapes, from Mumbai to Manhattan, and everywhere in between. Cities of the World: Extreme Spot the Difference features 42 stunning images of these metropolitan wonders. Designed to challenge experienced “spot-the-difference” puzzlers, these seemingly identical side-by-side photos each contain nearly 100 incongruities. From an obvious firework added to one skyline to a tricky-to-spot now-you-see-it-now-you-don’t bridge in the mid-ground of Manhattan, each find brings the puzzle closer to completion.

The perfect mental challenge to keep brain synapses firing, Cities of the World: Extreme Spot the Difference even includes a unique and reusable spotter’s grid that lies over the pages and can be written on and erased, keeping the beautiful images pristine and ready to be used time and time again.