Passed under and over and often overlooked, Chicago’s bridges are as architecturally significant as its skyscrapers. New walking tours run by civil engineer Jim Phillips explain the history, design and mechanics of 18 bridges spanning the Chicago River.

Popular 90-minute tours run Fridays through Mondays and start at the Beaux Arts-style Michigan Avenue Bridge at the McCormick Bridgehouse and Chicago River Museum. The cost: $20 per person. (312) 540-0696; chicagoloopbridges.com [1]