The first fully scenicked large layout I ever saw was in the home of the owner of the first train store I remember going to, Charlie Farmer of Elmira NY.
After that were a number of layouts from both MR and RMC. Particularly the Crooked Mountain Lines, the Sunset Valley, the V&O and the Clinchfield. The NEB&W which I was fortunate enough to see in person.
In addition, my family was on a trip to England. We had a couple of hours to kill so we happened upon a local show in Harrogate where I was blown away by what they could do in a small portable layout.
Martin