My all time favorite model RR to visit is the San Diego Museum. Not sure of the numbers but the floor space must be somewhere on the shy side of 10,000 sq ft with several really great RRs in various scales. All very well done by a variety of highly dedicated folks.
Do not think big portable race tracks but these are very large by long by tall, even two stories in one case with an ascending walkway around a scale Tehachapie loop.
Even a neat Brio room where you can get down on the floor with the grandkids and play choo-choo on an assortment of Brio layouts.
What I found interesting was the aprox 40' sq room room with three rail. Half of the shows attenders were in this one small area. It seems like the general public has a favorite son. Have been there on several occasions and each time the three rail room is very well attended while the hard core like me are studying the various aspects of the 0 scale, HO and N empires along the uncrowded aisles.
A must visit by any RRer. Allow at least a half day without troublesome tag a long non RRers. Let them visit the other attractions in this vast museum complex.