I love me my O-gauge tintype Marx sets from pre-war thru the 1950s--and so does Mister Tristan (the 3 year old human being, not the blog). See here and here for previous posts with photos of some of my collection.
Anyway, I'm getting interested in what are called "garden trains," where you have a larger gauge set-up outdoors, running thru your landscaping. I'm just at the reading-about-it stage. If I proceed, my scale would not be as large as Walt's above, but I can see this being a lot of fun.
The connection to Ultrarunning is that I would try to model some of my favorite trail running sites. For example, the Annapolis Rocks site along the Appalachian Trail in MD. Also Chimney Rocks along the AT near my home here in PA.