RPG Trap Design

One of the things that I want to be better at, when I am designing D&D adventures, is designing traps. When I think about this, I think about Indiana Jones and the Last Crusade, where three traps and a puzzle are the focus of the action and do a lot for the story. Their solutions are embedded in the film’s themes and the stick in the mind when I think about the movie.

There are a lot of issues that come to mind when I try to come up with traps for a D&D adventure. I wanted to write out my thoughts on traps, just in case some of you have the same challenges designing your own adventures.

Previous Victims

Think about who built the trap, and why. Are they still maintaining it regularly? Checking for dead victims and clearing their bodies out? If so, are there signs of their passage? Maybe they don’t clean the blood-stains completely enough, and this could be a hint for the PCs as they explore. If there is a pit-trap, for example, with spikes at the bottom, is anyone climbing down there to remove the dead bodies? Is there a trapdoor down below to allow access? If so, the PCs might climb down, find the trapdoor, and circumvent other traps, or ambush whoever it is that created the traps in the first place.

If the bodies aren’t being cleared, there might be some obvious hints that there is a trap nearby. These hints could be great foreshadowing, actually. There is a fantastic illustration in the 5E DMG, seen below, that is an example of what I have in mind here. The wizard is reaching toward what is obviously a trap, and you can clearly see the bloody marks and hand-prints from previous victims. This trap might even require a Wisdom save to force yourself to reach in there without shaking or hesitating. But I love the idea of bloody marks, or the stench of decaying bodies beneath a trapped floor, warning the PCs that something bad is ahead.

This foreshadowing effect of non-maintained traps also solves the problem of PCs calling for Perception rolls every 10 feet as the move through a dungeon. If you are exploring an ancient tomb, defended by traps that re-arm themselves and don’t require maintenance, then you’ll run into previous victims, and might even get some hints as to what threats await.

How Does It Actually Work?

Things like “pressure plate” are kind of thrown around, without always thinking about they really work. I’m not saying you have to go get an engineering degree to come up with traps for your D&D game, but take a moment to think through how the trap could work. If nothing else, when your PCs start prying it apart to disable it, you’ll be able to give a good description.

But, if nothing else, how does the trigger activate? Does the pressure plate work a lever, or is there magic that simply detects when someone steps on a particular stone in the floor? Is the poison needle in the lock spring-loaded, or does it use the force of turning the knob, or is it just hidden in the mechanism so that whey you reach to push the door open, you prick yourself?

Think about how it resets, and think about what it means if the trap is a one-off. If the trap can’t reset itself, then it will only work once, and either you will need NPCs to periodically reset the trap, or you will be able to follow a path of dead predecessors and unlucky adventurers pretty far into the dungeon before you encounter a trap you’ll have to bypass.

I would say, rather than see these as problems, make them features. Built the menace in your deathdrap dungeon by showing a dozen previous adventurers (their equipment stripped of course) who died in gruesome and horrific ways before the PCs ever arrived. Maybe describe them as apparently more accomplished and powerful than the PCs. Maybe one of them was famous, or a member of an Adventurer’s Guild that the PCs recognize. Then, suddenly, no dead bodies. Now the PCs know they’re in for it.

Not Built to Wound

Much as I hate to just kill PCs outright with a single die-roll, one has to consider the fact that traps would not be build to wound intruders in most cases. They would be designed to kill. Now, PCs are obviously extraordinary people, but in the Monster Manual most basic humanoid NPCs listed in the back have two hit dice, meaning any given trap, even the most basic sort, should do at least 10 damage on average. This would be enough to kill curious farmhands, and who would go into the trouble of building a trap when someone who isn’t even an adventurer could just take the damage and continue? This means, in DMG terms, that we’re looking at at least 2d10 damage for any trap that isn’t designed to be a nuisance, or a warning, or only designed to stop kobold children.

Other Senses

Think about how your traps function – what is necessary? And then what would those necessary elements smell like? Sound like? Would they have an effect on the texture of the walls, ceiling or floor? Would they kill off the local lichen that has covered other passages? Would they attract insects?

I had fun looking up what various highly flammable fluids would smell like when building a trap in a previous game. So the PCs encountered this sweet, chemical smell in a certain corridor, and didn’t know what to make of it (failed Intelligence: Nature check). So when they set it off, they got doused and then set on fire.

But if there is, say, ten gallons of highly corrosive acid suspended above the PCs’ heads, ready to sluice down onto them and melt their faces, what does all that acid smell like? Is it in an airtight container? If not, it’ll be possible to smell it, or even hear it bubbling menacingly. (I know acid doesn’t just sit there bubbling, but let me remind you, we are playing pretend.)

Simple Magic

Speaking of playing pretend – given the resources available to the average D&D dungeon-builder, I’d expect a lot more magical traps than mechanical ones. Your usual D&D world has little or no gunpowder, but a significant number of people who can throw fireballs. Even for first-level casters, you have magic missiles that can’t miss, and alarm spells that can’t be circumvented, simple illusions, color sprays and thunder waves. Why build a complex mechanism to push people over a ledge when you can just have a triggered thunder wave to shove them off? The DMG doesn’t have a lot of details around how to build traps, and only a few examples, but I’d take as a starting-point any spell with an interesting effect in the PHB. Why have darts shooting at your PCs when there could be rays of frost, both damaging them and slowing their escape? Why have a poisoned needle in a lock’s mechanism when it could just trigger a poison spray? And at higher levels, I’d expect far worse.

The Trap Is People!

In a previous game, I planned a series of ‘traps’ that were actually just kobold-like creatures being assholes. They had constructed these no-win situations where it looked like the PCs could get their hands on treasure, or even objects that were needed to solve a puzzle-door that would enable them to continue, but while they tried to get to these things, there would be creatures in various parts of the room, fully prepared, shooting them or lighting them on fire or flinging things at them.

So imagine even a group without a lot of resources at their disposal, but they know that adventurers will come to try and take what they have, and they have weeks, or months, or hears to decide how to mess with those adventurers. Having the trap be people has the added benefit of letting them taunt the PCs while they damage and hinder them. Of course, if you choose this option, when the PCs finally get their hands on the culprits, expect some epic butchery.

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