FEEL THE POWER of the largest operating steam locomotive in the world, the Union Pacific 4-6-6-4 Challenger #3985 as it pounds away the miles between Wyoming and California pulling an excursion train for a national railroad convention.  Among the many locomotive and train sounds are spectacular pass-by recordings, three in-the-cab perspectives and an "audio tour" of some of the operating features. 27 tracks of pure steam power!