As an active member of the SGMA, I constructed these mountain modules several years back to add some vertical interest to our modular layout. If you have ever seen these in person, they are painted somewhat like the mountains on the Carail layout. They were painted by my father, a well known local artist. They have a center slot but out of their bottoms for maintenance.
This year in Syracuse, my sons had their own table, but took some time out to play in the SGMA layout. Let's just say that they enjoyed watching these trains from INSIDE the mountains, a view most children will never see.
Far and away the best reason to be interested in trains. . . .the future.
p.s. the smaller one is Alex (4), the medium one is Thomas (6) and the largest one is Charlie, a very good friend.