The world's largest steam engine is making its final stop in Colorado tomorrow, in the town of Eaton. Union Pacific's Big Boy made a stop in Greeley today around 1 p.m. Train people love the "Big Boy." Yes, they do. The locomotives were only made for a few years during the mid-1900s and there is only one of them still running. If you aren't able to see "Big Boy" this week, it is going to come back next year to celebrate America's 250th anniversary.