Interesting question. I was wondering when it would come up. Although I enjoy running trains, I really consider the trains and track as the "thread" for my scenery designs. As a former graphic designer, My obvious interest is the scenery design and realism thereof. The hours spent on building structures, of finding elements to simulate trees and shrubs and ground cover, my true love. I can think of no other hobby that allows an individual to focus on so many aspects of the hobby. True fullfilment.
Allan