In a large dungeon or megadungeon you can never be perfectly prepared. No one has the time—or the patience or dedication—to prepare hundreds of diﬀerent encounter areas.
When the characters are in danger of wandering out of the area you have ﬂeshed out, disaster looms. At this point, if you are tired or stressed you might panic. This means either the session comes to a juddering halt or the quality of your GMing plummets dramatically. Neither situation is ideal.
I’ve found the following tactics handy in providing the illusion of detail without ﬂogging myself to death preparing countless areas and encounters (some of which inevitably will never be used).
Have a small pool of detailed random encounters to hand. Such encounters enable you to slow down a party’s progress if they are heading in a direction you have not yet detailed. These encounters shouldn't be deadly, they just have to slow the players down to let you prepare the areas ahead. Dungeon wanderers (gelatinous cubes, small bands of humanoids and the like) or even other bands of adventurers make great add-in encounters. Chance encounters with other adventurers don’t even have to end in combat!
The actions of burrowing monsters, the side eﬀects of powerful spells or even just earth tremors and earthquakes can temporarily block oﬀ access to part of a dungeon. If it’s rained recently, ﬂooding can also create an area of all but impassable terrain for lower-level characters. Once you have prepared the relevant dungeon sections, remove the blockage—the ﬂood waters subside, the powerful spell eﬀect wears oﬀ, the dungeon denizens clear the rockfall themselves and so on.
As eﬀective as a blockage, placing a monster or pack of monsters the party know they can’t defeat in their path is a great way of diverting a rampaging band of adventurers. Use this tactic carefully, and give the characters every chance to retreat or realise what lies ahead. If the characters don’t realise how powerful the monsters are, things can go horribly wrong.
Sub-Levels and Side Complexes
Dropping in a small side complex of rooms, or access to a self-contained sub-level, can divert the party long enough to give you time to prepare the upcoming area. These “mini-dungeons” don’t need to be fully ﬂeshed out. You just need enough details to wing it. The players will likely never know as long as the monsters and treasure make sense in relation to the rest of the dungeon.
Cry for Help
In a similar vein to Random Encounters, the party might encounter someone who desperately needs their help. Perhaps, they encounter an escaped prisoner or slave who needs to be escorted to the surface. Alternatively, they could meet a lone adventurer searching for his companions who just happened to go missing in the part of the dungeon you have prepared. If you use this strategy, be sure to reward the characters for their aid. The NPC might even become a regular ﬁxture in the campaign!
I love dungeon dressing. I love it so much. Raging Swan Press has released many books and articles on the subject.
In the context of the illusion of detail, dungeon dressing fulﬁls two critical functions: it slows down the characters (as they investigate the mutilated body, strange graﬃti daubed in blood or whatever) and helps you add depth and verisimilitude to the dungeon.
Dungeon dressing rocks.
The Final Word
When using these tactics, don’t use only one or two. Mix things up so the characters don’t realise what you are doing. Using a mix of the above tactics helps you maintain the players’ suspension of disbelief and keeps the session running smoothly. It also saves you time and stress.
Using the tactics listed above to create the illusion of detail is not about subverting or changing the characters' ability to make meaningful choices in the dungeon. Creating the illusion of detail is all about giving you breathing space while keeping the game going.
If you really don't want to use these tactics, you have two choices: tell the characters you haven't prepared the areas ahead or draw the session to a close. Neither of these works for me, but they might work for you.