I remember as a kid, 7-10 years old, of going to Toyland in Detroit's Hudson's Department Store in downtown Detroit.  I think it was on the 10th floor and only at Christmas.  Santa Claus, of course, was up there.

The layouts were customized each year - looked huge, but probably only 10' x 30' or so.   The unique thing I remember was that the outer level loops were 3-rail Lionel and upper levels winding around the mountains were usually the American Flyer 2-rail. 

I remember vaguely that the train showcases were pretty close to the layout.  I always enjoyed the Dinky Toy displays too.  The Hudson building has been torn down.   (At the time, 1998, it was the largest building ever to be imploded.)