(Re-)Stocking the Megadungeon: Empty

Once again, I am between campaigns, and once again, the urge to craft a megadungeon settles upon me.

I've done a bit of logistical planning of this current incarnation of my megadungeon, and have already determined that the first level, or entrance level, will feature 100 encounter areas.  Not rooms or chambers, necessarily, but areas.  In the end, it boils down to the same thing.

Filling those 100 areas is easier than it seems, if only because I lean on this table from Moldvay's Basic:

Others have done the math breaking down likelihood of various combinations over 100 dice rolls, but I'll summarize:

6 traps 'guarding' treasure

8 traps

8 unguarded treasures

12 monsters

16 specials

17 monsters with treasure

and 33 areas are empty.  

For the uninitiated, empty doesn't mean empty, it simply means the empty area contains no specified monster, special, trap, or treasure.  Veteran players should be automatically suspicious of a truly empty - devoid of dust and debris - chamber or room.  And rightfully so, as that suggests a monster, a trap, or a poorly conceived illusion.

This means that empty areas can be used for other purposes beyond burning resources and garnering additional wandering monster checks, especially if said area is a larger corridor or chamber with multiple entrances.  These empty rooms can provide respite if defensible and out of the way, or fallback positions in case of PC retreat.  If well-hidden behind secret doors, empty rooms might even be turned into waystations and resupply points by canny PCs.

Mostly, though, these empty rooms can - and should - be used to build up the history and reality of the megadungeon.  Use these rooms to let PCs discover evidence of past explorers, current denizens, or ancient mysteries.  This becomes simpler once the Monsters are (mostly) decided upon and placed, but sometimes these empty rooms can feed into those entries, instead.

Imagine discovering the shed skin of a snake that is apparently 30' feet or more longer.  Then later catching a distinct reptilian smell in the air.  

Other discoveries like large bloody footprints, a burned out fire and discarded food remnants, monster, animal, or adventurer scat, broken weapons and armor, and/or torch and candle stubs all tell a story.  Forgotten or lost useful items (although these may overlap with the Treasure or Special entries) are always welcomed by the magpie adventurers.  

Graffiti is another fine way of giving life (and occasional clues) to your world, as reading 'watch the water that is not water, and beware the basilisk' warns of potential dangers, while 'kilroy was here' warns of rival adventurers (or history-obsessed DMs).

Kalman is no Bargle, but he is still a threat.  Maybe he dwells within the dungeon alongside the graffiti.

Of course, sometimes random is better than design, so a custom table of dungeon detritus and dressing can be rolled on, or one of the published or online forms can be used.  

What all this means is that these 'empty' rooms may need keyed, as well, even if only with a one- or two-sentence description of what is there or just a few words or drawings on the map itself.  Yet empty rooms cannot be keyed if they are not there, so incorporate empty rooms to your dungeons, if only to further emphasize the Exploration pillar of D&D.  Besides, without empty rooms, it can be difficult to show the sheer size of the megadungeon in game.