If there's a train enthusiast in your life you won't want to miss this.

The world's largest steam locomotive left Wisconsin on Friday morning, bound for an afternoon stop in West Chicago.

According to CNN, the steam engine is back on the rails for the first time in 60 years and is the only operational Big Boy steam engine in the world. The train is on a trip across the Midwest to mark the 150th anniversary of the completion of the Transcontinental Railroad in 1869.

Union Pacific's schedule says the Big Boy will head west to Rochelle, Illinois, on Tuesday morning and will traverse Iowa, with stops that include Clinton, Cedar Rapids and Des Moines.

Only 25 of the Big Boy engines were built, in the early 1940s, primarily for hauling freight through the Wasatch Mountains in northeast Utah, according to Trains magazine.

After logging more than 1 million miles on Western railroads, engine No. 4014 was retired in 1961 and given to a chapter of the Railway and Locomotive Historical Society in Southern California according to CNN.

Union Pacific engineers have been doing restoration work on the 600-ton locomotive 4014 for the past two years in Cheyenne, Wyoming.

Union Pacific is posting updates on the train's location on its Twitter feed.

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