A Comprehensive Guide to Secret Doors

People will draw an 'S' on their dungeon map many times before they start thinking about what makes a good secret door.

Secret doors are an absolute cornerstone of D&D, and yet they don't get as much attention as other common dungeon elements.  I guess they're a little boring (compared to traps and magic swords).

Here's the thing: secret doors are an excellent opportunity for OSR-style gameplay.  A secret door is a common dungeoneering problem that is usually solved through observation and intuitive solutions (as opposed to system mastery, or having silver weapons).

Sidenote: Courtney has written a couple of good posts but I wanted to write my own.  

Tip #1 - If it's essential, don't put it behind a secret door.

Sort of general disclaimer: if finishing a dungeon requires the PCs to go past a door, don't make it a secret door.  The reward behind a secret door should be optional.  This avoids frustration and allows secret doors to perform their primary function: rewarding players for skillful dungeoneering.

(The secondary function of a secret door is to be cool as fuck; don't underestimate the impact when the wall of the cramped cellar swings away to reveal a forest of glowing fungi.)

by Peter Mullen

Obvious Door, Hidden Lever

These is my preferred archetype.  There's three parts to this.

The Door: A sealed door makes the PCs suspect a trigger is nearby.

The Trigger: They search the room to find the trigger.  

The Reward: They are rewarded for opening the door.

The Door is obvious.  It might be a huge metal door with no way to open it except to discover the mechanism.  It could be a stout wooden trap door that can be smashed (at the cost of noise and time).  It might be a wall of flame that they can jump through at the cost of damaging themselves.

An obvious door allows the players to focus their search here.  Instead of searching every nook and cranny of the whole dungeon, obvious cues like this allow the players to focus their time and attention on key places.  

The Trigger is hidden.  This is the part that tests the players.  They can deduce the trigger from clues, figure out comprehensive ways to search the room, or discover some way to interact with it.  This is the fun part, because this is the challenge.  In the dungeon, this is where the gameplay is.  (One of many.)

Remember that the trigger doesn't have to be super-hidden.  Simple triggers can hide modest rewards.  That's also fun.

The Reward can be:

• Loot.
• A shortcut to deeper levels.
• An ambush opportunity.
• A place to spy on the orcs.
• A way to slip inside the statue so you can shout at the cultists and impersonate their god.

Hidden Door, Hidden Lever

I don't like these as much.  

To be sure, they have both precedent and placement reasons, but they're easier to miss since the players are more likely to walk past them.  

True, you can train you players that you have lots of hidden doors in your dungeons, but then you are also training them to spend their time fully investigating every room in the dungeon.  I'd rather train my players to investigate the things that seem interesting (since they often are more interesting).  We can cover more dungeon that way, and I spend less time saying "you don't find anything".

Hidden Door, Obvious Lever

I guess these exist?  You pull a lever, hear a grinding sound, and then you have to backtrack to find where the door opened.

These are only fun if you have a good wandering monster table, you want to show players have rooms have changed since they were last visited, or time is one of the fun challenges in this dungeon (e.g. the dungeon is literally sinking in the ocean, do we really have time to backtrack).

Meh.

Semi-hidden Doors

There is an opportunity here to make it a two-step process, with doors that are semi-hidden and then triggers that are more hidden.  It's also a gradient--you can have a semi-hidden door with a semi-hidden trigger.

Heck, you can even have a semi-hidden door with no trigger (i.e. push to open).  These are also good.

Semi-hidden doors are defined as ones where the DM uses cues (breadcrumbs) to lead the PCs to discovery of the hidden door, or at least to get them to suspect its existence (so they'll know to search the room).  

Cues for a Semi-Hidden Door (roll a d10 or a d12)

1. Scuff marks or footprints.
2. Hollow sounds as you walk across it.
3. Old stains, or fresh blood dripping through the seams.
4. Breezes.
5. Sounds.
6. Smells.
7. Temperature changes.
8. Anomalous architecture (e.g. discolored stone, sagging walls).
9. A dead end in a hallway (especially if the hallway seems well-traveled).
10. Obviously passable surfaces: waterfalls, curtains.
11. Seeing a creature flee into a seemingly dead-end room.
12. Put a clue on a map.

Using Maps to Indicate Secret Doors

Remember, the whole point of having obvious doors is so players know to concentrate their attention in a specific area.  The clue doesn't have to come from the room itself.  It can come from the mouth of an NPC

Sometimes the clue comes from the map.  OSR dungeoneering is full of shit like this, which is why you'll see so many people making these meticulous maps (as opposed to a quick diagram of which rooms connected by lines).  Examples:

• Symmetry implies a room. (e.g. the lower floor seems to share a floorplan, yet this room lacks a counterpart on this floor.)
• The shape of the adjacent rooms (and exterior wall?) imply that a room should be here.
• Necessity: if you know the tower has 5 floors, then you know there must be a way up from the fourth floor.

Triggers (d20)

Remember that a trigger might just unlock a door, not necessarily open it automatically.  The trigger might also need to be held (if you want to be a dick).

A lot of these options aren't necessarily exclusive.  You could combine some of them into better triggers.

Obscured By Object

1. Recessed lever behind painting.

2. Switch beneath rug or behind tapestry.

Challenging Environment

Some of these can get into puzzle territory.  Good.

3. Hidden underneath really heavy statue.

3.1 A pressure plate is only depressed when a really heavy statue is placed on it.  The statue may be in a different room.

4. Trigger located beneath the surface of the boiling mud.

Integrated into Object

5. The door unlocks when the statue is rotated to point at the door.

6. The trigger is in the hinges of a different door.  When the first door is fully closed, the secret door unlocks.

7. Pull the torch sconce, ya turkey.

Instructional/Riddle

8. The offering bowl is full of ancient blood stains.  Fill the bowl with blood.

9. The mural shows dancers at a festival.  Imitate their dance.

10. The plinth reads "ten men's length, ten men's strength.  Ten men can't break it, a child can carry it."  Place a rope on the plint.

Simultaneous Triggers

11. Both discolored bricks must be pushed simultaneously for the door to open.

Trial-and-Error

This covers situations where there are multiple things to try, and the players just have to guess which one is the correct one until they figure it out.  And because there has to be a cost for wrong answers, pulling the wrong lever usually results in a trap being set off.

Sometimes there's a pattern or a clue that allows intelligent players to deduce which lever is the correct one.  In this case, pulling all the levers is just the (costly) brute-force solution.

If there's no clues to which is the correct lever, then the puzzle becomes: how do we protect ourselves from whatever trap is going to trigger when we pull the wrong lever?  (Hint: use a 10' pole.)

This is actually getting away from strict secret doors and into the trap/puzzle spectrum.

12. Three levers.  The first causes acid to fall from an (obviously discolored) crack in the ceiling.  The second is electrified.  And the third opens the door.

Symmetry

One of the common types of Zelda puzzles.

13. The room contains a lit torch and an unlit torch.  The door unlocks when both torches are lit.

14. The room contains a dozen levers, arranged at different heights.  The door unlocks when all of the levers are set to the 'up' position.

Brute Force

This covers kinds of switches where the biggest limit is how much time the PCs are willing to use.  At worst, this can be pixel bitching.  At best, this is a resource-management choice.

DM: It'll take you 90 in-game minutes to attempt all the combinations.  Do you still want to do it?

Player: Yeah, sure.  Go ahead, roll your wandering monster checks.

And in this case, finding the trigger is only as fun as making the cost-benefit analysis of cost vs. reward.  

Like the trial-and-error triggers, this can be an acceptable brute force solution for puzzles where the players didn't find the clue.

Example. The door will not open unless the correct demon's name is spoken.  The walls are covered with the names of thousands of demons, including the correct one.

Anomalous Architecture

These are basically solved by noticing that something is out-of-place and then interacting with it.  If a player says "I inspect the X closely; tell me more about it" they're 90% of the way there.

15. One of the bricks is a different color than the others.  Push it.

16. A small hole in the wall is revealed to be very deep.  The trigger is 5' deep in the hole, and must be activated with a pole or spear shaft.

17. Investigation reveals that the chandelier chain goes into the ceiling.  Pull the chandelier.

18. Outside the castle window, a small bullseye can be seen on one of the exterior bricks.  Hit it with an arrow.

Repetition

19. One of the bricks is a different color than the others.  Push it three times in a row.

False Backs / Nested

20. The first secret door reveals a small chamber full of garbage.  If the garbage is cleared away, one of the bricks can be seen to jut from the wall.  Pushing this brick opens the second, actual secret door.

21. The cabinet has a false back.  The false back can only be opened when the cabinet is closed.

Deductive

There's also cases where a party might realize late in a dungeon, based on some new evidence, that they might have missed a secret area early in the dungeon.

For example, they might see multiple blue tiles throughout the dungeon.  Later one, they see where a blue tile has been smashed and an empty cavity revealed.  Now they can go back, smash all the blue tiles they saw earlier, and grab the small treasures inside.

(I'm not really sure how to code this one, and since it relies on dungeon design, it doesn't really belong on a "d20 secret doors" generator.

by Peter Mullen

Bad Secret Doors

Just Checks

Roll a Perception Check.  Roll a Search Check.  Roll a Disable Devices Check.

If this is all you are doing, then you are only challenging the character sheet, not the player.  This is boring.

Pixel Bitching

Basically, when the player spends a lot of time doing a boring task to track down some trigger, with no clues to lead you to it.

Here's a bunch of identical tiles.  Roll for each one.

Here's a room full of boring things to investigate.  Spend time describing to me how you're going to investigate each one.

At best, this is a Brute Force trigger (see above).  

Tip #2 - When you expect players to be searching a room carefully, choose carefully how many interesting features you want to put in that room.

I try to limit myself to no more than 2 or 3 significant things in each room.  

Sometimes a room has lots of objects in it by requirement, e.g. a kitchen.  Be careful hiding triggers in kitchens.  The players will remove every drawer and break the sink before they notice the switch at the back of the oven.

Searching  dense room isn't necessarily bad--and it may even be fun if the kitchen is interesting--but it does take time.  Just be mindful of it.

Compare that to a room that is empty except for two discolored bricks and an obvious secret door.  The players will come in, and one of two things will happen.

(a) They'll figure out that they need to push both bricks simultaneously.

(b) They won't figure it out, and they'll move on to the next room.

Either way, it probably won't take as long as the kitchen scenario.  And if they think of the solution later in the dungeon, they can always come back.

Final Note

Spend a moment to think about what is behind the secret door.  A party is usually pretty invested in finding the trigger for a secret door (it's an activity anyone can participate in), so when the door finally swings open, you'll probably have their attention.

Lastly, the reward doesn't have to be treasure.  It can be something bad, like a bunch of zombies.  Zombies are their own reward.

If you still want some more secret door stuff, here's a couple more other sites.

Raging Swan

Dragon's Flagon