Imagine this...
 
Christmas morning finds you up before the family.  It is still before sunup, but the glow on the horizon promises a bright Christmas day.  Throwing on a bathrobe, you head down for a cup of coffee.  As you glance into the living room, your eyes widen:  The tree, presents, furniture, everything is moved, crushed into the dining room...  In their place sits a large C-track layout on a green blanket on the floor, covering the room from wall-to-wall.  In one corner lies a big city with a 10-track Kopfbahnhof (End-station), the catenary cross-spans stretching a good two feet to catch all the catenary wires.  Across from the station near the center of the room sits a large diesel, electric and steam engine BW, complete with coaling tower, turntable, and twelve-stall roundhouse.  Over on one side lies an eight-track freight yard, complete with gravity track (Ablaufberg).  Nearby is a harbor scene, with a pair of 7051 cranes ready to unload the large ship model sitting at the dock.  At the other end of the room a secondary line winds its way into a mountainous region, where two tree-covered mountains, a village on each one, are connected by a high bridge.  Below, the mainline passes between these mountains and disappears around one of them, with the bridge far above.  A second station sits to your left, with passing tracks and a small freight depot.  A small circus scene lies nearby.  Everywhere you look there are signals, old semaphore types, and newer light signals.  Trees are everywhere, as are houses and roads, filled with cars and trucks and figures.  Catenary adorns all the tracks.  But it isn't the tracks or scenery which catches your eye.  It is the mix of rolling stock that takes your breath away.  In one of the stations sits the original Northlander model.  Nearby sit the Orient Express and Lorelei trains.  A freight train of thirty or so high-capacity ore cars waits dutifully near the freight yard for its turn to course around the layout.  An ICE and IC, both in full prototypical length, jut out from the end-station platforms.  Sitting in front of the roundhouse are every steam engine imaginable, from the newest BR01 incarnation to the big Borsig and the streamlined 03.10.  Even the King Ludwig train, majestically parked on a siding, catches your eye.  Below you sit the controls to this layout.  It is a fully digital layout, you surmise (a new PC sits adjacent to the layout, though there are also a half-dozen handheld controllers), with each switch and uncoupler digitally operated. 
 
With trembling hands you pick up the two extension cord plugs and plug them into the wall outlet.  Immediately the layout is ablaze in lights, red and green from the signals, white from streetlights.  The carousel begins spinning.  Somewhere (you can't even tell) a church bell recording starts playing.  The first puffs of smoke begin to emerge from the stacks of the steam engines.  Then, as if on cue, the trains begin moving, slowly at first, then picking up steam.  The delightful SSSSHHHHH sound of Märklin trains in motion fills the room.  You marvel at the sounds of the class 151 electrics as the brakes squeal, and strain to hear the hum of the V200's diesel, which pulls a rake of blue and green D-zug coaches behind it.
 
A class 260 switcher pushes a string of cars up the hump, which automatically uncouple at the top and roll to their respective sidings.  A beige and red TEE train behind an E03 pulls into the end station.  As you watch, a second E03 pulls out of the BW, couples to the end of the TEE, and pulls it slowly back out onto the main line.  The first E03 then follows dutifully and switches into the BW.
 
The chuff-chuff-chuff of a steam engine draws your attention to the Rheingold with its blue and gold cars.  It appears around the side of the mountain behind an 03 just as a Swiss Crocodile crosses the bridge high overhead, a string of Swiss freight cars in tow.  A local passenger train, three silverfish cars behind a blue 110, pulls into a siding at the second of the two stations and stops at the red semaphore signal.  The Northlander flies through on the main line.  After a minute, the signal changes, and the local pulls back out onto the main.  In the opposite direction, an E18 with a dozen green era III coaches slows into the same station.
 
The cranes at the harbor dutifully unload the ship's cargo into a group of gondolas.  Finally filled, a BR55 pulls the gondolas out of the harbor to begin their trek around the layout, finally returning to the harbor to be unloaded back into the ship. 
 
As you watch in awe, a strange sensation comes over you.  You become dizzy, disoriented.  As you begin to lose your balance and your eyes cloud over, you reach out for something to hold onto.  Strange, your hand finds a large pole, a feature your living room has never had!  As you regain your senses you are met with the most spectacular sight you have ever beheld.  Your eyes widen as you look up to see a Brawa (you are *sure* of it) lamppost towering over you.  A quick look around confirms your suspicion- you have been reduced to 1/72 scale, and are standing *in the middle* of this beautiful layout!  On your right the crossing gates go down and a train of Swedish wood-sided cars glides by.  To your left a BR23 growls out of the roundhouse.  You scamper over and watch it take a turn on the turntable.  As it slowly backs past you you grab a hand iron, grateful to Märklin for their detail, and hoist yourself into the cab.  The sound from the motor is deafening, but it doesn't seem to bother you.  You hold on for dear life as the steam loco backs into the large end-station.  It couples to the front of the Lorelei train, and before you know it, you are whisking around the layout with a quintuplet of blue and red coaches in tow.  The blue-and-cream Rheingold with its 24cm cars, including the observation car, streaks by you in the opposite direction.  To the right you watch the BR55 with the gondolas slow into the harbor once again.  The buzz of an uncoupler draws your attention to another siding, where an era I freight is just uncoupling a pair of boxcars at the brewery.  Ahead the signal is green, and you begin the climb into the hills and mountains on that end of the layout.  Almost silently the ICE Sinus glides by in the other direction...
 
The view from up here on the mountain is amazing, and you look out over the vastness of this beautiful layout.  Where to go next?  Maybe you could watch the cranes unload the ship, then ride along on the freight train, or perhaps sit in front of the roundhouse and watch your favorite engines pull in and out...  Your train crosses over the high bridge.  Far below you watch "Le Capitole" head towards the Kopfbahnhof.  The Lorelei train slows into the station on the far mountain, and you contemplate getting off.  Before you can decide you are moving again, past rows and rows of enormous HO scale trees.  Then, without warning, day turns to night as you enter a tunnel.  The noise from the engine and cars is unbearable, and you press your hands to your ears.  It doesn't help, and you begin to feel dizzy and faint.  Slowly you slip to the floor of the engine...
 
All is quiet.  You blink once, twice in the darkness.  It is no longer the hard plastic of the engine cab that you feel below you, but the soft sheets on your bed.  You get up, still in disbelief, and stumble into the bathroom.  It was so real!  How could it have been a dream? 
 
Sleep won't come soon, you know, and though it's only 3:00 a.m. you slip out of the bedroom and down to the living room.  It is still Christmas Eve, and the tree stands quietly in the darkened corner.  You look around the room, at the mound of presents under the tree.  Your eyes light upon one familiar wrapped box- it's the premium digital starter set you bought for yourself, and next to it sit several suspicious wrapped boxes that could only be tracks and switches.  A twinkle begins to gleam in your eyes.  Without making a sound, you tip-toe across the room to the coffee table.  It slides easily as you pull it into the dining room...