"Take a piece of graph paper. Draw a box hemming in 26x26 squares. Write 1-26 across the left side, one number in each square along the outside. Write A-Z along the top similarly. Above this write LEVEL ONE. This is your Level Map.
On the next sheet of graph paper, draw a box hemming in 30x30 squares. Above, write LEVEL ONE M-13. Each square in this Local Map is 10' across. That means each Local Map is 300' x 300'. This square Local Map corresponds exactly to square M-13 on your Level Map. That is, on your Level Map, find the M row and run your finger across to the 13th column. That is your M-13 Local Square.
26 Local Maps x 300' per Local Map equals 7,800' x 7,800' per dungeon level, or about 2.1 sqare miles."
The above quote is from a comment 1d30 made here. he goes on to point out that 30x30 is the area of the grid in the one page dungeon template! Zooming out like this isn't a staggering concept, wilderness areas are often mapped at different scales right? This is like running with a map and battlemats but zooming out instead of in. Or you could use the two scales of maps and battlemaps and have all three scales.
Here's a picture of that extruded into three dimensions:
Each of the small cubes is a one page dungeon.
The Caves of Chaos would fit inside 4 of those cubes.
What excites me about this idea is the potential it opens up to create a mega-dungeon, without tons and tons of upfront work on the DMs part. Instead, the DM can place important rooms/regions, and leave places in between to fill in at the table on the fly. More about this idea here. Al's idea here reminds me of the Nolli maps. Giambattista Nolli made a fantastic map of Rome in the 1700s where the important public buildings and plazas are drawn in detail and al other buildings are simply shaded in.
Of course it could all be mapped and stocked ahead of time, but that would be crazy, unless you have some friends help!
I'll have more to say about this later.