Terry Johnson's layout (OGR DVD #7) when seen in person. A light/sound/trains extravaganza for sure! Tornados, lightning, star-studded heavens, low-flying jet fly-by (be sure your dentures are well in place for THAT one!), and some mechanical wizardry that is truly inspiring! 'And that's a fact,...Jack!' (With apologies to Jack Rogers, who arranged for me and my wife to see Terry's layout, and Sy Robertson!)
But, the earliest layout I saw some 60 years ago...and it's still around...that became seared in my brain was/is Roadside America. And the coolest/craziest thing about it was, what I call, the 'switchless switches'...fake turnouts that led to spurs loaded with appropriate cars parked by appropriate structures. For a kid who treasured his two O22 switches on his layout, and felt empowered every time he threw the lever to activate them, these 'fakes' were, well, a dumbfounding disappointment....later in life to be recognized as a brilliant, economic alternative.
Then there was a G scale layout set up on the Queen Mary in Long Beach, CA, for the annual G show back in 1997, I believe, that featured a dismembered soul lying across the railroad track complete with pools of blood and gore front-and-center for all the squeamish to see! It was just fun to stand aside and watch as the show folks discovered this one....particularly the gals!!
+ Lots more.
KD