Steam - UP 4014 "Big Boy"

UP 4014 is the world's largest operating steam locomotive. It was built by American Locomotive Company (Alco) in November 1941 for the Union Pacific Railroad and 1 of 3 surviving locomotives in UP's steam fleet.  All locomotives are stored in UP's roundhouse at Cheyenne, WY.
Additional insights on the Big Boy's can be found on the UP steam page 2.