Dungeon exploration game movement rules generally assume you are:
- trying to move quietly
- trying to map
- try to spot hidden danger or hidden anything
Let's talk about that first one, moving quietly - and more broadly, how do you sneak in a dungeon?
It seems like most people assume - for surprise, for wandering monsters, and especially for their own characters, that they're moving pretty quietly, stealthily, and generally make it hard to detect them. Not only that, but that they can see and hear pretty far themselves. How true is all of that?
How easy is it to move through an underground tunnel quietly?
"A base movement rate of 120' in 10 minutes may seem slow, but it assumes that the players are mapping carefully, searching, and trying to be quiet."
- Dungeons & Dragons Basic Rulebook, ed. Tom Moldvay, p. B19
Moldvay pegs you at a movement rate of 1 yard every 15 seconds, which is pretty slow if you think about it - it's not a march, it's a very quiet and slow movement rate. Presumably, it's abstracted between speeds much like a lot of D&D is abstracted - overall, you get 120' every 10 minutes, which includes some quicker movement and stopping to look at things and draw your map. So you aren't burning along at a high pace, you're trying to be quiet. No word on how far that sound carries, that I can find anyway.
AD&D is a little more harsh. The DMG implies you're making some noise - thieves move at the normal rate silently if they make their Moving Silently check (well, if the GM does). Special versions of the Ring of Invisibility make you silent, too - as do Boots of Elvenkind. But heavy gear can make you noisy, and light get singled out as easy to spot under discussion of pursuit:
NOISE: Characters in metal armor can be heard for 90', hard boots can be heard at 60', relatively quiet movement can be
heard at 30'."
- AD&D Dungeon Masters Guide, Gary Gygax, p. 68
So you can only be heard out to 30' if you're quiet, out to 60' clicking along in those hard boots you bought, and out to 90' if you're in metal armor - mail and plate wearers, look out.
No surprise, GURPS addresses this sort of thing directly, with a (pretty easy) rule for hearing distance. GURPS Underground Adventures has some more general rules for this sort of thing - specifically how far sound and light carry in an underground setting. Not surprisingly, sound can carry pretty damn far. Stone makes it echo, which can make localizing the sound hard (-2 to the roll in GURPS, per Underground Adventures p. 10) but tunnels carry the sound along pretty well.
While GURPS is pretty generous, in my opinion, about how loud walking is (half Move is a "normal conversation" and Stealth rolls work without extra penalties at Move 1 aka 1 yard per second) it's counteracted by how hard it can be to localize the sound. Not only that, it singles out combat and cane travel - aka tapping on the floor. Like, say, how a 10' pole would work. Rhythmic or a-rhythmic, tapping is pretty loud - and needs to be if you're using it to hear your way places or hear covered pit traps.
So you're giving up your best chance at not being heard by doing your best to avoid pit traps, tripwires, false floors, and unseen dropoffs. It's tap and likely be heard, or don't tap and take your chances with the floor.
Encumbrance matters for Stealth - you suffer your encumbrance level as a penalty to the roll. So heavy armor gets you, too, in GURPS. And either combat were blows are struck or tapping makes Stealth rolls impossible and makes it significantly easier to hear you!
Environmental factors will come up here, too. GURPS gives a +4 for most caves because they are quiet; but a megadungeon, for example, or occupied caves with monsters in them, will never really be quiet. I personally zero it out - the distant bangs, groans, creaks, drips, scrapes, etc. are enough to obscure some noises, but aren't so loud that they'll obscure them completely.
All in all, avoiding making noise is pretty hard, even without talking or fighting.
"LIGHT: Straight line of sight is near infinite, any corner cuts distance to 60'."
- AD&D Dungeon Masters Guide, Gary Gygax, p. 68
"Treat the light as in in plain sight to distance observers who have a clear view of it: +10 to Vision rolls to see it"
- GURPS Underground Adventures, p. 10
In either case, this works out to be the same thing - if they have line-of-sight on your light source, they're going to see you. Which mean all the sneaking in the world won't help unless you've extinguished your light sources and gotten away from other light sources. Fortunately (and GURPS points this out), light helps you see within its radius but obscures what's outside its radius. It's the "blinded by your campfire" issue - you adjust to the better light source and it effectively blinds you to what's outside of its radius.
This is one I find people forget the most - they'll move quietly, communicate by gesture, and otherwise minimize their sounds - as they sneak past the door with a half-dozen magical sources of extremely bright light. Oops.
"ODORS: Normal scent can be detected by creatures hunting or tracking by scent for several hours - even in a dungeon setting. Scent can be masked with various things - mustard powder, oil of citronella, crushed stinging nettle, etc."
- AD&D Dungeon Masters Guide, Gary Gygax, p. 68
I like how it singles out scents. Although I think there is a mistake waiting to happen there - yes, citronella will mask your odor, but it's a different and strong odor. It might easily alert something even if it convinced smell-hunting unintelligent monsters not to bother you because you don't smell like food. Active camouflage like this can backfire pretty easily. A better approach would seem to be either match your smell to nearby creatures (ala Disguise (Animals) in GURPS) or eliminating it (the No-Smell spell in GURPS).
But yeah, smell is potentially important.
GURPS Basic Set doesn't spend much time on smell, but I think it's worth having any monster that can smell make a roll if stinky stuff comes by - adventurers burning torches, stinking of sweat and blood, fresh meat, etc.
"If anyone sneaks up on us, J'zargo will smell them coming. Or he might not. We'll see."
- J'Zargo the Khajit, Skyrim
Discriminatory Smell is a perfect case for this - with it, a critter might detect what's coming, and tell the difference between "delver stinking of sweat and tension and metal" and "one of those juicy giant rats." Don't forget to check if they smell the adventurers coming - and it's yet another dimension a sneaky group needs to use.
In a fantasy game especially, other senses matter. Monsters might have Vibration Sense and feel you coming. They might have Detect Life (Precise) and sense your presence no matter how quiet you are. They may have magical triggers to alert them to your proximity. Even the sneakiest of folks can fall prey to supernatural detection. If the monsters have it, you need to have an idea how close anyone could get before they just get detected. And those trying to sneak up need to figure out clever counters . . .
We Speak in Sign Language
Coupled with a good way to see in the dark, this isn't bad. But it's limited, and all the PCs will need to learn it. Even then, it's hard to fight quietly . . . which brings us to combat.
What about combat?
Combat sounds will carry everywhere. The odds that you're quietly sneaking up to a room, quietly forcing the door, and/or quietly neutralizing monsters is pretty low. Especially that last bit - it's hard to kill quietly.
In Basic D&D, if you aren't quiet in the first place, your chance of a surprise drops to nil:
"EXAMPLES: A party is no likely to surprise a monster behind a closed door if the party has just fought a battle near that door. A party will not surprise a monster if the attempt to open the door fails (even once!)"
- Dungeons & Dragons Basic Rulebook, ed. Tom Moldvay, p. B23
Same in GURPS - a fight counts at least as "loud conversation" (no penalty at 4 yards), more (presumably no penalty at 8 yards) if metal armor is struck. -0 at 8 yards means it's only -3 to hear at 512 yards if you're in a normal 10' x 10' dungeon corridor. Oops, there goes the element of surprise in the orc complex. Once they've heard you, it's not that much harder (despite the -2 above) to locate the sound and figure out what it is. Even if they don't, kiss Total Surprise goodbye, and Partial Surprise might go bye-bye too if they're actively preparing to fight.
Gunfire is ridiculously loud (see GURPS High-Tech for details), so if you're using primitive guns or really loud magic (Thunderclap, any Explosive Spells, etc.), it's going to wake up the whole damn dungeon.
So fighting and weapon use is noisy.
Whether denizens will react or not is a different issue - maybe they're like me, and are used to some "outside noises" - police cars, neighbors, the fire truck heading out, the train rolling by. Or maybe they're in a quiet zone and hyper-sensitive. Maybe they known from experience that bangs and crashes and shouts of combat are a sign that easy food is around, or that extreme danger approaches. But between light, sound, and smell, it seems hard to stay truly quiet in the dungeon.
There is a nice bit here of Rob Kuntz discussing playing Robilar solo in Gary Gygax's game. The encounters were set up for groups, with the assumption that a big noisy group is coming. He used magic to achieve surprise by staying quiet and unseen (and presumably using some kind of light-free vision source) and attacking by surprise. This is something that just isn't terribly reasonable in a group.
Not without magic - which I'll cover in Part II - and possibly good gear and tactics, covered in Part III.