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Modular Rules & Procedures for Cairn

  • Adapted from the Cairn Adventurer’s Guide Adam Hensley, used with permission.
  • This content is licensed under CC-BY-SA 4.0
  • This document lists some optional, modularly-designed rules & procedures for Cairn (and should be adaptable to most other OSR-adjacent games with minimal tinkering).
  • These rules are designed to be plug-n-play, so just grab what you like and discard the rest.
  • These rules are not critical to the structure of the game and can be discarded or ignored at certain points in your game.

Dungeon Exploration

Note: L is used in reference to player level. Example: A level 2 player would see Ld6 and roll 2d6.


A dungeon turn is 10 minutes. Dungeon exploration can be turned into a subsystem of managing resources, making strategic decisions, and structuring the dungeon crawl into a sort of mini-game. There is an element of pushing your luck as you spend more time searching, checking for hidden things, and lingering in dangerous locations. Time spent always has a cost, and that cost is provoking an encounter roll. These encounters can involve running into monsters, but can also challenge or reward the party in other ways.

Sequence of Player Per Turn

  1. Encounter roll: GM makes a d6 encounter roll once every few rounds, or at their discretion.
  2. Actions: The party decides what action to take. (e.g. moving, searching, listening, entering or exiting rooms).
  3. Description: GM describes & resolves what happens. If encounters were rolled, they happen here. If (1) was rolled on the encounter die, make a reaction roll and proceed from there.
  4. End of turn: GM updates time, and management of light, food, need to rest, or any sort of usage dice rolls can be made.

Dungeon Turn Movement

  • Players can move carefully about 200 ft. in a 10 minute turn. Players moving careful spot signs of all traps. Traps should be designed to be disarmed or subverted with ingenuity and creative thinking using common sense and items, not skills and rolls.
  • Players can quickly move 600 ft. in a 10-minute turn. Players moving quickly may get a chance to roll under WIL to notice a trap (GM discretion). Otherwise, they may trigger a trap (usually 1-2 on a d6, adjust as necessary for trap deadliness)


  • A quick search takes 1 minute, covers roughly a 30x30’ space, and reveals only the most obvious information.
  • A detailed search takes 10 minutes (1 round), covers roughly a 30x30’ space, and reveals most hidden information, at the GM’s discretion.
  • You can replace 30x30 with small, medium, and large rooms, and require additional turns to complete a detailed search.

Loaded Encounter Roll

Roll a d6 encounter dice every 2 or 3 rounds (at your discretion, adjust as needed). Only a roll of 1 will result in an encounter, and they won’t always be hostile. Roll the reaction dice to see their disposition, and remember that they’re already doing something.

  1. Encounter (roll on encounter table or choose, roll reactions + wants)
  2. Sign (Clue, “spoor”, track, abandoned lair, scent, victim, droppings, etc.)
  3. Locality (context-dependent timer, water rising, ritual completing, The party’s surroundings shift or escalate in some way.)
  4. Exhaustion (rest next round or deprived)
  5. Expiration (Ongoing effects end, light usage roll, resource usage, bellies rumble.)
  6. Discovery or Treasure (The party finds something interesting and possibly beneficial.)


Torches, lanterns, and other radial sources of light illuminate 40’ clearly and provide dim outlines and shadows for a further 40’. In the dark, light sources are visible miles away. Standard torches will last about 6 turns, or 1 hour, before they burn out. If expiration is rolled on the encounter die, consider prematurely snuffing out a torch or rolling a usage die.


When the PCs encounter an NPC whose reaction to the party is not obvious, the Warden may roll 2d6 and consult the following table:

2 3-5 6-8 9-11 12
Hostile Wary Curious Friendly Helpful

What Do They Want?

d10 Want Description
1 Food or Aid They’re hungry. You can distract them with rations, point them towards corpses, cast a food illusion. They could be hurt and need healing.
2 Gold They want d100 gold x the players’ level. This could be a tax, a toll, tribute, tith, or they could just be greedy bastards, or easily distracted by shiny baubles.
3 Treasure They want a number of items equal to the players’ level. Scrolls and potions count here as well. Excellent pairings can result in their friendship as allies.
4 Random Item Roll a random item from a random PC’s sheet, they want that for some reason.
5 Territory This is their territory, they will defend it, but mostly they just want you to leave or prove why you should be able to pass through.
6 Information They want to know about a rival faction, nearby NPC or monster, or dungeon landmark or location.
7 Help They need something from further in the dungeon, or from a nearby wilderness location. They may want you to kill other monsters in the dungeon or clear out a hex. They may be haunting the area and can only leave when their quest is fulfilled.
8 Trade They have a random item from each category on the equipment list (one piece of armor, one weapon, one piece of equipment, etc.) and they’re willing to trade those items or save them. All trades made inside the dungeon are at a higher markup that you’ll find in town.
9 Mission They’re in service to the closest NPC in the dungeon (or GM choice) and whatever that NPC wants, this monster is on a mission to help achieve that aim.
10 Direction They’re lost and are looking for directions out, or for someone to escort them to a safe area.

Wilderness Exploration

Hex Crawling

Each hex represents 6 miles. An adventuring day is divided into 6 turns of approximately 4 hours each. Two of these phases, approximately 8 hours, must be spent sleeping in order to avoid becoming deprived. In each turn, the following procedure is followed:

  1. Action: The party decides on one exploration action for that turn.
  2. Event Roll: The GM rolls on the event die for encounters and other random events.
  3. Resolution: The action and event rolls are resolved.

Exploration Actions

The party may choose one of the following standard actions each 4-hour turn.

  1. Travel: passing through a hex and into an adjacent one. On roads marked on the map, the party travels through two hexes (three if mounted). Off-road, one hex is traversed. There is also a 2-in-6 chance, when traveling off-road, of getting lost. This is increased to 3-in-6 in hexes classified as difficult terrain. An experienced woodsman decreases the chance of getting lost by 1-in-6. If players get lost, they will need to spend the next turn using the “search” action to reorient themselves. The effects of getting lost are rolling a d6, assigning a number to each side of the current hex, and moving the players one hex off course in that direction.
  2. Explore: Looking for interesting features within a hex. There is a 4-in-6 chance of discovering the main location in the hex description. Difficult terrain reduces this to 3-in-6. An experienced woodsman increases the chance by 1-in-6.
  3. Search: Looking for something which was previously encountered in a hex. The basic chance is 5-in-6 or 4-in-6 in difficult terrain. An experienced woodsman, tracker, or navigator increases the chance by 1-in-6.
  4. Interact: Staying in the current location (e.g. exploring a dungeon, town, etc).
  5. Camp: Resting and/or sleeping.
  6. Forage: Hunt, fish, or forage for food. There is a basic 3-in-6 chance of success. An experienced hunter, angler, or woodsman increases the chance.

Event Roll

The DM rolls 1d6 and consults the table appropriate to the party’s location.

  1. Encounter: Roll on an encounter table for that terrain type or location.
  2. Sign: Clue, spoor, or indication of nearby encounter, locality, hidden feature, or information about a nearby hex.
  3. Locality: Shifts in weather, terrain, or other local changes.
  4. Expiration: Exhaustion (Rest next turn or add 1 fatigue), Hunger (Eat a ration or add 1 fatigue), or another resource is needed.
  5. Discovery: Discover something useful such as food, treasure, or other resources.
  6. Hidden Feature: The main feature of the hex is discovered, or, choose or roll randomly for a unique hex feature from a random table. Options include small dungeons, secret areas, factions, etc.

Shield Splintering

Players can opt to absorb all of the damage from one attack in exchange for their shield breaking.

Leveling Up

Experience Points (XP)

Gain a new level every 1000 XP. Roll 1d6 x new level to determine your new HP. If lower than current HP, increase by new level. Example: If you are level 1 with 3 HP, and hit level 2, then you roll 1 and 2 on the 2d6 HP roll, take 2 HP (your new level) for a new total of 5 HP.

Optionally, you can increase the experience needed to level if needed. Increments of +500 at each level are a good starting point.

Gaining XP

Experience points are gained at a rate of 1 XP for every 1 gold (or your game’s standard currency) retrieved and returned to the safety of a town or your base of operations.

Ability Scores

Each time you level up, re-roll your Ability Scores with 3d6. If the results are higher than your current scores, increase by 1.


You can spend your hard-earned gold on experiences rather than on things. Carousing lets you double-dip your experience by spending it at a 1-1 ratio. The more you spend, the more impactful or eventful your experience. Carousing represents having a good time or in some other way an experience involving spending your wealth to blow off steam. Alter these tables or add your own mishaps and fortunes. They generally represent getting into shenanigans while inebriated but can also be sober celebratory outcomes.

Carousing Roll

Declare the amount of gold you’re spending and roll 2d6 to see how your evening went.

2d6 Result
2-5 Experience is gained. However, you’ve all made fools of yourself in some manner. Roll on the carousing mishaps table.
6-9 Experience is gained.
10+ Experience is gained. You’ve all had a stroke of good luck! Roll on the carousing fortunes table!

Mishaps & Fortunes

Roll 1d6 + 1 for every 200gp you carouse with. More decadent binges come with the potential of more volatile or legendary events.

d10 Mishap  
1 Start a brawl. You all are involved in a brawl that gets out of control. Start the next adventure with a black eye and -1 STR per level. The local tavern keeper is no longer quite as amicable. Jackpot! One of you strikes it rich at the gambling tables! Gain level x 100 gold.
2 Minor misunderstanding with local authorities that you’re unable to smooth over. You all spend the next 1d6 days in jail. Now seen as local troublemakers. Gain a local reputation as the life of a party! Those of ill repute are much more friendly and see you as one of their own.
3 One of you insulted a local person of rank. They will hold a grudge unless you all publicly apologize and humiliate yourself before them. Whoa what a trip! The strange powder you sniffed revealed mystic truths about the universe. Young people in the settlement see you as cool and not one of the squares. (Optional: gain a random spell or generate a Maze Rats spell, either one-use or permanent.)
4 Hangover from hell. The first 2d6 hours adventuring the next day are done with disadvantage to all STR saves. Well fed, well rested, and ready to go! The next day of adventuring all saves are done with advantage.
5 Gambling binge. Your party owes a collective debt equal to roughly half the amount spent carousing to someone you’d rather not own money to. Citizens arrest! You catch some criminal in the act and are able to restrain them until the authorities arrive. You are seen as heroes by the settlement for a short time.
6 You’ve ruined the local economy! Your excess spending means that all prices are now double until next session. The local blacksmith, due to your influx of cash, has been able to craft or order an exquisite weapon that he’s willing to sell to your party for a normal price.
7 Major misunderstanding with local authorities. All equipment is confiscated until fines and bribes totaling 1d6 x 100 gold is paid. The local clergy see your party as protectors of the settlement. They offer you a blessing before your next adventure.
8 While in a drunken stupor and a spot of trouble, you sought refuge in a church. They took care of you but now as repayment have begun hounding you to perform a charitable act. Impressed by your ability to drink for days and keep standing, a local hireling of high repute is willing to join you on your next adventure if you wish at no initial cost.
9 Bad Investment. Invest d100% of your gold in some smooth-tongued merchant’s scheme. Turns out it’s a sham. One of the town merchants flees. Killer Investment! Invest all your spare cash in some smooth-tongued merchant’s scheme. Turns out it’s real! It returns 50% profits next d4 sessions.
10 Due to a lost game of darts and a few inflammatory remarks at the tavern, you make bitter enemies with a local rival adventuring party. Local celebrity. Your ability to carouse with the common folk has led them to see you as one of their own. The peasants of the settlement are thankful to have you around. You receive free room and board in this settlement of average quality.
11 Beaten and robbed. You are waylaid by a bunch of thugs during your drunken carousing. Loose Ld6x100 coins. Hot Goss. Your time spent carousing has let you in on some juicy gossip. You learn one major secret about a person in authority.
12 The roof! The roof! The roof is on fire! Accidentally start a conflagration Roll 1d6 twice. (1-2) burn down your favorite inn (3-5) some other den of ill repute is reduced to ash (6) a big chunk of town goes up in smoke. (1-2) no one knows it was you guys (3-5) one other person knows you did it (6) everybody knows. Heroic Carousing! It was a night of truly epic debauchery. Everyone roll a d6 to see how your legend grew. (1) Re-roll HP for your level, take new result if higher, increase by 1 if lower. (2) Gain 1 STR (3) Gain 1 DEX (4) Gain 1 WIL, (5) Gain a random spell book (6) Gain Ld6 x 100 GP.

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