Dungeon Exploration Procedures

As The Alexandrian pointed out recently, the 4e DM Guides express no procedures for handling exploration. This is perhaps not surprising from a team whose focus in published adventures was on small, easily navigated lair-assault style dungeons and used skill challenges to represent overland travel. But it means that new DMs and players were given no tools for dealing with exploration of large and/or complex underground environments or actual exploration of the wilderness.

Thumbing through the 5e core books, I can see that the situation hasn’t improved very much.

If you want a experience that treats dungeon exploration as more than finding the transition to the next combat encounter, there are mechanical procedures which were developed at the dawn of D&D, and have evolved and improved in the intervening decades, which are available to help you.

Wandering Monsters

First, let’s talk about wandering monsters. In a dungeon consisting of five rooms separated by thirty foot hallways, wandering monsters have no role. Each hallway takes one or two rounds to cross, depending on character speed. Each room takes three or four rounds to defeat the monsters, plus 5 minutes for a short rest. The whole dungeon can be cleared and explored in about half an hour of in-game time, and the environment is small enough that every monster is accounted for. And there is no need to apply time pressure, and nothing to be gained from doing so.

On the other hand, when an environment is large enough that it will require several sessions to clear; when resources must be carefully conserved in order to cover more ground; and when the environment is inherently hostile and characters need to proceed with caution; then wandering monsters can serve an important purpose.

Wandering monsters make choices as to whether to attempt particular tasks meaningful. Noisy tasks, like battering down doors, can attract monsters. Lengthy tasks, like repeated attempts to pick a lock, or carefully searching rooms, or mapping, also increase the risk of encountering monsters.

The modern systems developed in corners of the OSR are more flexible than those early systems, but for players new to the concept it probably makes sense to start with the older systems and work our way forward.

Time and Distance

Early systems stressed the importance of accurate keeping of in-game time by the DM, which regulated periodic wandering monster checks. In 1e, the basic unit of time for exploration was the “turn”, which consisted of 10 minutes. Every set number of turns a die would be rolled to determine if an encounter occurred. The 1e DMG characteristically forgets to say how often such checks occur, or what die is rolled for the check. But from my recollection of the published adventures, checks could occur every 1 to 3 turns, and a d6, d8 or d12 could be rolled, with a “1” indicating an encounter. I noticed that several of Gygax’ dungeons used a d12 check every turn, which is closely equivalent to a d6 check every turn.

Note that in our standard 4e five room dungeon that would be the equivalent of a single d6 check once during the dungeon. Which isn’t worth the effort of making a wandering monster table.

Now, a PC can cover a lot of ground in 10 minutes at normal walking speed. So one of the conceits of 1e was that, if they wanted to map an area as they went, the effective speed of the party was greatly reduced. A PC party enencumbered by equipment or armour and making a map as they go could expect to travel 120′ of corridors every 10 minutes. A party following a map could travel 600′, and a party wandering without either using a map or making one, but still having a modicum of caution, could travel 1200′. Note a real human being walking at 3.1 mph for 10 minutes will cover 2728′. Also note that a PC with a move of 6 squares per 6 second combat round would travel 3000 per 10 minutes.

The thing about this conceit is it provides encounters at a frequency which, with some development over the decades, has proven to work. So we want to work toward that level of frequency, that is, a check for every 120′ to 360′ travelled.

The best way to do this is to tie it to player choices. You want a map of where you’ve been? You want to travel with a degree of stealth? You want to keep a lookout for traps as you go? Then expect to travel 5 x movement rate squares per turn. Otherwise you have to rely on memory to navigate, you attract monsters because of noise, and you fall in pits regularly. Your choice.

Now, if this seems too slow, you have a couple of options.  First of all, you can mess with the duration of a turn. Lots of 4e durations are in increments of 5 minutes. But the PCs will pay for that when they double the chance of encounters when taking other actions, like casting rituals. So when you discuss it with them, point that out.  Also, this messes with the assumptions of the much improved “hazard die” system, which I will discuss later.  You will see what I mean when I get there.

Alternatively, you can use distance instead of time when making wandering monster checks during corridor exploration.  After all, monsters exist in space, there could be a correlation between distance travelled and frequency of encounters for a given density of monster population. You would still use time for time-consuming activities like picking locks and casting rituals, but when exploring corridors you could make a check every, say, 50 squares.

However, this approach has a significant problem.  It punishes characters who flee from battle by increasing the number of encounters they are likely to face.  If you are trying to run more of an old-school dungeon, you want the players to feel free to run away when necessary.  There are already a lot of disincentives to flee:  player stubbornness, opportunity attack rules, risk of getting lost (no mapping while you run), risk of running into undetected traps.  But running into a wandering encounter while you are fleeing one where you were already outmatched is a big one.

Personally, I prefer the time-based method.  If you think about it, accurate mapping would take a great deal of time.  Take a 120′ hall (24 squares).  First, someone has to traverse it slowly to check it for traps.  Take a step, probe with a 10′ pole, take another step, probe with a 10′ pole.  That’s going to take at least twice al long as walking the same distance, probably longer.  Also assume characters are checking walls and ceilings.  Then, once you know it is safe to step wherever you want, someone needs to pace off the length of the dungeon, and draw it on a map.  And the party is doing this while trying to be stealthy and not draw attention to itself.

So lets say the clearing phase is at a movement rate of 1, and the mapping phase is at a movement rate of 2 (for stealth), in which case this process will take 36 rounds, or 3.6 minutes.  Assuming the ordinary number of distractions, and marking special features, doors, intersections, and so forth, rounding that up to 5 minutes does not sound unreasonable.  Add to that the fun of writing all that down accurately in a world that hasn’t invested graph paper, possibly using a ruler, while juggling a torch, or miscounting steps and having to measure again, and on average it could take even longer.  Heck, in real life, things always take longer than you think.

So let’s start with an assumption that, with a movement rate of 6 and no modifiers, the party moves 3000′ or 600 squares per 10 minutes.  If the party uses stealth we divide that number by 2.  If the party maps we divide by 2.  If the party checks for traps we divide by 5.  These divisors are cumulative, so if the party is stealthy and careful but not mapping it travels 600 ÷ 2 ÷ 5 = 60 squares per turn, but if it also maps it travels 30 squares per turn.

So movement per turn in squares = movement rate x 100 ÷ stealth modifier (if any) ÷ mapping modifier (if any) ÷ care modifier (if any).  Or just assume that the party is doing all three, and that movement per turn = movement rate x 5.

Time Taken for Other Actions

So that covers movement, but what about other actions?  According to the 4e Players Handbook, searching a 15′ x 15′ area only takes 1 minute.  However, if you have ever lost your keys or your phone you probably don’t buy this.  In 1e searching a 20′ x 20′ area takes a full turn, which probably makes more sense if you assume the characters are pushing a prodding, looking for loose bricks and flagstones that things might be hidden behind, or cracks in the wall that might be secret doors, or for tripwires and pressure plates that might be traps.

But in practice the general rule should be this:  most significant actions should be assumed, on average, to take a turn.  In other words, in most instances, the wandering die roll should be triggered by the decision to do a thing.  Although things relating to skill checks that can be repeated could be shorter.  Making a single attempt to pick a lock could take a minute, or five minutes, and have to be repeated if it fails; taking 20 on picking a lock could take 10 minutes and guarantee a wandering monster check.  Bashing a door down doesn’t take long but could create noise, so it gets a check (with the monster showing up at the tail end of any resulting combat).  Searching a room gets a check; searching a large room might take two or more checks.  You get the idea.  Just use your judgment.

Basic Procedure

So your basic procedure for handling time and movement is:

  • Figure out what precautions the party is taking, and calculate speed per turn using the method suggested above.
  • Every time a significant out-of-combat action is taken for which no time is specified, assume a turn has passed.
  • Every turn, check for wandering monsters.  Roll 1d6:  on a roll of “1”, a monster is encountered.  Encountered monsters begin the encounter 4-24 (2d6 x 2) squares away.

If this seems like too many monsters (on average it would be one per hour), increase the time between checks or the size of the die.

That is the basic system, and you should play with that on its own for a while to get used to it.  Once you are used to this procedure, and you think you might want to  kick up your game a notch, you should consider an innovation on this procedure which was been developed by certain OSR bloggers.

The Hazard Die

I first learned of the Hazard Die system from Hack & Slash, who adapted it from Necropraxis.  The Hack & Slash article is particularly good and I recommend you read it, since it discusses aspects of the system in more detail than I am going to go into here.

The impact of the Hazard Die is to simultaneously give the dungeon a little more life, and remove the bookkeeping from certain timed events while randomizing them.  It assumes that, on average, torches burn for 1 hour before they go out, and lanterns burn for 4 hours before they need to be refueled.  It also assumes that dungeon exploration is exhausting and takes its toll.

The Hazard Die system has several applications, but at its core, a d6 is rolled, with the following results:

  1. Party suffers a Setback
  2. Party suffers from Fatigue
  3. Expiration of ongoing conditions
  4. Change related to Locality
  5. Perception of some clue
  6. Party receives an Advantage, or nothing happens.

Necropraxis has a PDF which describes this in more detail for a variety situations.  When used in the context of the dungeon, my modification of this for 4e is as follows:

  1. Monster Encounter (i.e. Setback)
  2. Party must rest for 1 turn or suffer Fatigue in the form of losing a healing surge.
  3. Torches begin to Expire.  Fresh torches begin emitting dim light.  Torches which are already dim burn out.
  4. Torches, lanterns and sunrods Expire.  Torches expire as above, lanterns burn a quarter of their fuel (or an eighth if you are using 4e durations), sunrods lose a quarter of their life.
  5. PCs Perceive sign of a monster:  tracks, bellowing roars, scat, claw marks, etc.  Roll on your wandering monster table to determine which monster they are perceiving.
  6. Local dungeon effect.  Earthquake, flooding, sounds in the distance, that sort of thing.  This can be some sort of transformative local effect, like an earthquake, cave-in or flooding, or some sort of clue to the dungeon, like sounds in the distance.  You should probably prepare a random table beforehand (six entries should be plenty), unless you are good at making these things up on the fly.  If you are unprepared, have nothing happen instead.

Note the expiration of light sources is only really relevant in a megadungeon or extended underdark adventure where conservation of light resources is a real factor; otherwise this can be ignored.  I also have other uses for #4 which I may go into in a future post.

Also note that there are times when you will want to use a simple wandering monster check instead of a Hazard Die roll.  This occurs when the party does something to draw attention to itself – like banging on things or blowing them up, or encountering shriekers – which are likely to attract monsters but do not result in the expenditure of time and consequent expiration of light sources and the like.

Procedure Using Hazard Die

So a modified dungeon exploration procedure would be:

  • Figure out what precautions the party is taking, and calculate speed per turn using either method suggested above.
  • Every time a significant out-of-combat action is taken for which no time is specified, assume a turn has passed.
  • Every turn, roll a Hazard Die (1d6):
    1. Monster Encounter, consult wandering monster table.
    2. Monster sign, consult wandering monster table.
    3. Rest for 1 turn or lose a healing surge.
    4. Fresh torches become dim; dim torches burn out.
    5. Torches expire as #4 above;  lanterns burn a quarter of their fuel; sunrods lose a quarter of their life.
    6. Local dungeon effect.
  • If the party draws attention to itself, check for wandering monsters.  Roll 1d6:  on a roll of “1”, a monster is encountered.
  • Encountered monsters begin the encounter 4-24 (2d6 x 2) squares away.



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