"Caves! We love Caves!" or 2d20, natural cave hazards.

This post was inspired by this post from the "Disoriented Ranger" blog.
Go read that post it's interesting

So your  players are working their way through some caverns and you feel they are not yet at one with the inherent danger of life below ground. It's time to throw a random natural hazard their way.

Natural hazards are defined by being non-fantastic. A field of giant sentient mushrooms that puff out rainbow colored rot spores are cool. They are not a natural hazard.

The entries on this chart are things that could be in any hallway of any cave and don't necessarily require their own map entries.

I will include notes about equipment that may be needed to  traverse the obstacle, however I will not include details like die checks, saves, or, damage values as they are system dependent. I will try to word these details in ways that are system agnostic. I will place equipment that might be used up or needed and  possible threats in (brackets) at the end of the entries.

Lastly, I did some reading and research for this list, but I am not a spelunker and I do not pretend to be expert on the subject.This list is build for fantasy games, not as a scholarly work. Please no "Sink holes don't work like that!" replies, because dragons don't work like that either.
What I did learn is this:

• Simply tripping over things is a big time hazard in caves, more so as you become more and more tired.
• Rock falls are also a major hazard particularly at cave entrances and any time a person is  repelling. I would say any Character caught by a rock fall should take significant damage. If the rock fall is major treat it like an area of effect spell, and save for half damage.
• The  cold and damp of caves can lead to hypotermia. How serious this is depends on how your game handles things like hypothermia. regardless if a person gets wet in a cave, things should get serious quickly. 
• I will not be dealing with getting lost on this chart, but that's obviously a big deal.
• I will not be dealing all that much with light on this chart but  it's also a very big deal.
• There is generally very little to eat in caves.
• Things like clothing , ropes, lanterns, food, water, poles, spikes, clips, hooks, and all of those items that a cave explorer might use are finite. Caves have a tendency to rip, break, consume, strand, loose, and, cut those items at a pretty high rate. Caving in a fantasy came could become as much about resource management as it is about fighting baddies.
• The features inside a cave should not be thought of as dangerous. Rather it is a universal feature of all caves that caves are dangerous. Danger should be all over when the players are delving in natural caves.
• Water is not just water.  It ruins torches period. Armored characters will have a hard time swimming if they have to. Worst of all however, It's cold it will get a characters clothing wet and lead to hypothermia if they don't dry out or change. Water is bad in caves avoid it.

From a GM's point of view fair warning should be given that some of these random items might  slightly alter the lay out of your cave. Some entries add  verticality others add some features like boulders or stalagmites. I tried not to make any of them all that earth shaking or map changing.

When your players are  running down that dark underground passage like a bunch Usain Bolt's ..
Roll 2d20

1. ROLL 2D20
2. This area is waste deep in mud. Fighting is nearly impossible movement is greatly slowed. The party is  open to attack form  enemies staying out of the mud. Passage over or around woudl be wiser than going through. (Rope) (Clothing) (Hypothermia) (Vulnerability)

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3. The  floor of this  area is only a thin mineral shelf. Knocking with a pole will detect the hollow areas and warn the party. Careful travel is possible, but undue activity, fighting, or reckless moment will result in the shelf collapsing sending every party member tumbling into to a dry grotto below. They characters will take medium damage from the  hard fall and have to climb back out.
   (Falling) (rope) (time)

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4. Great bunches of roots make it hard to pas through this area, they also denote being close to the surface, care should be taken to avoid a cave in. (poles)

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5. This section of cave contains several huge boulders that have collapsed in from above, they are wet and muddy, squeezing between them will be difficult. Characters in any armor heavier than leather will have to remove their armor to continue through these pinch points. Footing is also  precarious. (poles) (ropes) (resource management "armor")

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6. A five foot wide and  thirty foot deep wash runs right down the middle of this corridor. It was created by run off water surging down this passage some time in the distant past. The narrow ledges along the sides are precarious and  fragile.

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7. Lichens coat the damp floor and walls of this cave section making footing difficult especially if fighting. The pale damp plants also hide other tripping hazards. 

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8. Lichens coat the damp floor and walls of this cave section making footing difficult especially if fighting. The pale damp plants also hide a steep wash out that acts as a slide if any character happens over it.
   The slide is thirty feet but not overly rough causing at worst minor bruising, getting back out however will take ropes and effort.. (ropes)(climbing gear)(Involuntary relocation)

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9. a swift fall of water flows from the ceiling to floor on the left side of this passage. The water drains out of the floor as fast as in flows in , where the floor meets the wall there is a pinch hole that an unarmored person could negotiate. Any one attempting to do so in armor however will get stuck and drowned as per the rules of your choose system if not rescued. (ropes)(poles)(drowning)(hypothermia)

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10. Stalagmites and stalactites merge in this corridor making passage difficult for large characters with allot of pointy objects sticking off of their back packs.



looks safe enough lets go ...

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11. The surface of this corridor is very jagged and uneven. Not only does this make footing difficult it makes falling down harmful. Any fall should be treated as an attack, causing lacerations to the hands knees and body.

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12. The air is dank and stale here, there is no breeze. The room is at the top of a natural chimney light gasses collect here. Within a few minutes the oxygen in this room will being to be used up. lanterns will dim, breathing will become labored after that follow your games rules for slowly dying until the characters can move along out of the chimney or retreat from the room. (suffocation)

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13. This section of the cave is unsteady and shifting, formed by a recent collapse or perhaps being undercut by flowing water the party must pick it's way careful to avoid triggering any further cave ins.

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14. This  section of cave drops away in uneven ledges formed over eons of erosion. Traversing this area will require a bit of repelling on ropes and perhaps ladders. The party will have to take it slow or risk falling short distances onto jagged plateaus. (Ropes) (ladders) (climbing equipment)

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15. The area vault upwards into the darkness, innumerable cubbyholes and small openings have been carved into the walls by eroding limestone.
    The area is generaly clear but confusing. All of the small openings make for hundreds of ready ambush sights or hiding spots for  local creatures. (disorientating.)

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16. The floor of the cave transitions to loose and sandy, some where in this area is a narrow sink hole. If a character moves over that sink hole they will begin a slide of sand that may pull other characters down with them. This feature formed when loose sediments washed into this area over time. The water flows out  through the narrow sink hole leaving the silt deposited by the slower moving water behind. The nice thing is this acts as a giant sluice box, the characters might find rare minerals scattered about in the fine silt. The bad thing is that will keep them digging around until some one hits the sink hole. (Drowning in sand) (poles) (ropes)(Involuntary relocation)

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17. A narrow fissure in the passage produces a stiff breeze that could blow out torches. (Resource management Torches)

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18. The passage narrows to a pinch point several yards where the party must wallow on their stomachs through silty mud in a very narrow passage. Torches will not work except for the  first person through. The party must go single file. Armor heavier than leather will not fit. (resource management Armor / torches) (vulnerability)

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19. The ceiling in this area is very fragile, visibly so. Any passage at all may cause a cave in. The area can be barred down but it will take time and make noise that any nearby nasty will hear. (Cave in threat) (poles) (time) (May attract enemies)


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20. This room is shaped like a narrow cone and is elevated above the central corridor. There is a small hole or crack at the top of the cone.
    This natural vent was formed through the action of a long extinct geyser. Now it collects gasses at it's peek which slowly  filter out through the old vent.
    If a character decides to explore the   cone he or she will get a nasty surprise from the collection of methane that builds up at the top over time.
    The small explosion would be enough to do a bit of damage and knock the character back down distance back to the floor.
    (resource torch)(resource Ropes)(resource Eyebrows)(Cave in danger after explosion)(explosion damage)(alerts monsters)

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21. The corridor here is winding and turns in on it's self at several levels. The party will have to be careful not to get turned around.
    (disorientation)(vulnerability to ambush)

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22. This corridor falls away steeply into the darkness. It will be necessary for the party to create a tryolean traverse bridge the length of the corridor to cross it. This means one Party member will have to scale crossed using only spikes first. This is no small task and should be difficult and serious.
    (falling) (resource ropes) (time)

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23. This room is filled waste deep in sauna warm water, small selenite crystals line the floor of the pool. This is a double whammy the room is  warm and humid meaning character will become exhausted quickly and may suffer heat stroke , particular those in armor. After they clear this room their wet cloths will cool rapidly leaving them open to hypothermia. (hypothermia) (clothing) (exhaustion)

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24. A small stream runs through this hall Bisecting it. The stream is shallow but to wide to jump. Recent rains mean the  water is swift and could take a careless character off his or her feet. (falling) (hypothermia) (lost torches and other equipment)

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25. This tube like corridor has strange gutter like  features running along it's edge, the gutters are filled with stagnant water and create a barrier to characters hoping to reach any adjoining passages. (falling) (stank water)

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26. This  shaft is built up of several narrow ledges intersecting each other, only one character at a time may pass, and the climbing is difficult.
    (ropes) (ladders) (falling) (vulnerability)

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27. A large hollow blob shaped ball of ancient congealed lava nearly blocks the passage way. Small characters can fit around the Laval ball but others will have a difficult time. The lava ball is attached to the caverns ceiling and can be dislodged but it will take time and make considerable noise. (time) (Alerts enemies)

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28. This area features a pool of bright blue water resting in a shallow grotto. A plume of stone erupts form the nearest wall and  spreads out like a large mushroom to the waters edge.
    Any character that explores or walks on the plume of calcified runoff runs a risk of collapsing the canopy formation into the water.
    HERE
    (Falling) (hypothermia)

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29. A Deep chasm bisects this passage way a collapsed Stalactite bridges the gap. The  stalactite is damp and covered with lichens making footing difficult. Travelers would be wise to rope off.
    (falling) (time) (rope) 

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30. The passage falls away and a waterfall tumbles down from somewhere above. Characters will need to take their time and be sure not to loose their footing. A fall would be survivable but the climb out  will be laborious.
    (falling) (water) (time) (rope)


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31. The  floor here is covered by scree and old cave ins. Any fighting in their area will impose penalties on characters that are not accustomed to underground environments.
    (Dangerous footing)

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32. This area is inhabited  by thousands of harmless bats. Their guano is knee deep in several places, making passage through this  are very difficult and unpleasant.  Passage through this area casts up clouds of dried bat guano could cause illness or disease in  unwary characters.
    (disease) (slow travel) (Resource Clothing)

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33. This section contains a pool of water which looks like a blue hole plunging into unknown depths. Crossing it should be easy, exploring it would be extremely dangerous.
    (temptation) (clothing) (hypothermia)

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34. This area is a winding section of narrow braided corridors with many  sharp blind corners. Only one character may traverse the area at a time. (Vulnerability)

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35. This clear looking  corridor has a high concentration of Lodestone with in the walls. If the characters are lucky enough to have a compass liek devise it spins wildly while near this area.

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36. A flood sometime in the past deposited a  large tangle of debris in this corridor. Old tree limbs, stones, animal skeletons, and  anything else that could have washed down is in this pile of junk. It will have to be cleared before the party can continue.

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37. There is a narrow vertical opening in the floor of this corridor, it's depth is unknown and it's rimmed with  loose stone. If any one tries to repel into the shaft utmost care needs to be taken to avoid rock fall. The walls of the shaft are solid and take well to spikes and pinions. (ropes) (time) (falling) (Rock Fall)

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38. The trickling rivulets of water on the caves walls have become torrents, this section of the cave is slowly filling with water. The characters may have notices water marks on the walls before this point or they may not have, regardless they need to get to higher ground until the rain above passes. (drowning) (Hypothermia)

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39. The ceiling rock here is fragmented and loose, undue vibrations or even loud noise might cause a rock fall. This is detectable with a pole and regular tapping, if any one is doing it. (collapse)

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40. This area must be scaled, its a tall almost sheer wall or chimney where a waterfall once flowed. This will take time and effort. The first character to scale the wall will have to place spikes for the others to follow. It is very tall and sheer, falling should mean almost certain death.
    (falling) (Spikes) (rope) (time) (exhaustion)

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Helpful links I looked over:
Mit intro to caving
Very Basic into vertical caving 
Caves.org is about caves
Tryolean Traverse:
caving accidents Reports:
Check this out  virtual cave tours, gameable maps, weaponized calcite. 

hope you enjoyed the post.
Thanks for reading
Leave questions and comments in the dark gaping maw of the  sundered earth below.
Mark.