Architect I.M. Pei’s firm designed the 16th Street Mall so that, when seen from the air, the repeating pattern of red, white, and gray stone that makes up the pavement would resemble the markings on a diamondback rattlesnake. At ground level, though, visitors will focus instead on the movie theaters, stores, and restaurants along the 1.25-mile-long stretch of this mall. From the Denver Pavilions shopping center near its south end to Union Station and LoDo (Lower Downtown) at the north, you’ll find much to entertain you. A Free MallRide shuttle runs along the mall in case your shopping bags get too heavy.

It’s easy to miss, but hard to ignore. As you stroll the 16th Street Mall, head toward Curtis Street and go west down the north sidewalk of the 1500 block. As you walk you’ll hear sounds from below that just do not belong—farm animals, underground trains, rushing water and almost 100 other bizarre soundtracks. Sound Walk by Jim Green has been fooling and confusing pedestrians for over 20 years through tape recorders hidden in grates. What will you hear?

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