The "crawl-through" origin came about years and years ago when I was making mazes out of cardboard for my brother and his friend. I would theme the mazes mildly, mostly kind of a Halloween theme with pumpkin stickers, cheesy music, and blacklight bulbs. In 2004 when I was 14 at the time, I wanted to try doing something in l blacklight paint, and I chose to make a Haunted Mansion Holiday themed mazed after being inspired by Disneyland's Haunted Mansion attraction with the seasonal Nightmare Before Christmas overlay. The only thing was I needed a dark place for it to work, so under my 30" high 4 X 5' model railroad table seemed to work. But this blacklight Nightmare Before Christmas themed maze evetually turned into an attraction showcasing the blacklight painted figures and flats rather than a freak-out maze with blacklight props. The cousins, whom I made the blacklight show for, enjoyed going through it and the parents found out about it and they too squeezed through the tight path (this was before I set path envelope standards). It was such a hit that I did more of them, with a bigger table, and with each one getting better and better. Up until now, I've done Haunted Mansion Holiday, Pirates of the Caribbean, Submarine Voyage, the Enchanted Tiki Room, and Haunted Mansion.
Now in 2009, what was once the old cardboard maze idea is now a massive collection of shoebox dioramas on steroids (and this time with an even BIGGER table!). I've kept the "crawl-through" format all these years because that's part of the fun, and it won't take up that much space unlike a "walk-through".
In a nut shell, a "crawl-through" is a series of dioramas set under a table with a height low enough in which the guests are required to crawl through them in order to view the scenes. The dioramas are set under the table because of the available space and controllable atmosphere.