An open pit mine

It’s pretty easy to draw mine shaft maps as adventure sites — as I posted earlier, real maps are freely available and you can really just assume there is one main shaft per level with various side shafts and natural caves attached here & there.

But a lot of mining was (and is) done via open pits. Some really impressive ones can been seen online, with the most inspirational (for me) being this monstrosity of a diamond mine in the former USSR:

Photo from Wikipedia

I’m a bit of an ignoramus about higher math so I asked my brother, who actually understands calculus and all that occult stuff, to calculate how long the spiraling road into the mine should be, and how far a drop you’d have from each point. (This matters a lot if you want to break up sections for encounters and to be able to reasonably adjudicate how far it is to drop from one level to the next, etc. My gaming group includes two fricking engineers (one a geologist, no less!) and a physics & math teacher so I am a little wary of winging things like this!

Anyway he cautioned me that for stability the vertical slopes along the walls should really be slanted, not straight up and down, but it was easier for him to get rough numbers assuming the walls are straight up and down.  That makes a trickier climb and generally more dangerous road anyway so I’ll go with it!  I’d like for parts of the road to collapse.
He took my initial call for a hole about 300 yards across and 200 yards deep and, being a diabolical DM himself, decided to work the numbers to get 13 passes on the way down and for the bottom to be 666 feet down. Perfect.

So if we want to know how long each “loop” of the spiral should be, and how far each drop to the next level is, we need to take into account slope, and I went with a 5% grade so wheeled vehicles could reasonably have navigated it while it was in use. (I based this on the fact that Roman roads were generally around a 10% grade and modern wheelchair ramps are required by code to be 8.3% or less.) Tom suggested a 15′ wide road so two carts could pass each other. He estimates an ox-drawn cart would take 46 minutes to complete a descent (not going at the D&D exploration rare of 120′ per turn, obviously!).  The “floor” of the hole is about 50 feet across, and going from top to bottom, each pass’s length, and the drop to the next level, is summarized below: (sorry about poor WordPress formatting!)

Road section from top/start Approximate average radius of hole at this level Length of road segment Drop to the pass of road below Falling damage to the pass below (d6)
1 253’ 1590’ 80’ 8
2 238’ 1496’ 75’ 7
3 223’ 1402’ 70’ 7
4 208’ 1308’ 65’ 6
5 193’ 1213’ 61’ 6
6 178’ 1119’ 56’ 5
7 163’ 1025’ 51’ 5
8 148’ 931’ 47’ 4
9 133’ 836’ 42’ 4
10 118’ 742’ 37’ 3
11 103’ 648’ 32’ 3
12 88’ 554’ 28’ 2
13 73’ 459’ 23’ 2

One funny thing is that the “lower” levels — those closest to the surface and the entrance — will be very deadly on account of falling damages, even if you put weaker monsters there.

A spoiler might be that the party can generally see down into the pit, at least during the day. So I’d have some hoardings and shacks built along the road for cover/shelter for whatever inhabits that part, and it also occurs to me that smoke or better yet fog could obscure much of what lies below. There could also be passages/shafts/caves along the “road” to the bottom, with sidetracks and ambushes and as sources of wandering monsters. (Really this could be a megadungeon in itself, with hell itself at the bottom.)  The idea of the PCs taking “shortcuts” down 60 or 70 foot walls, and probably having to get around occasional collapses, is pretty cool too.  Flying and levitation spells or items would be a huge help!  But what loathsome monstrosities roost in such an eyrie?

But this open mine is cut into just one slope of Mount Telengard, with more traditional mine shafts (and very ancient crypt) cut into the side of another slope, and there is also a vast wooded area on another slope of the mountain, rumored to hold terrible, otherworldly monsters. So Mount Telengard should provide plenty of places to adventure…

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Published in: on October 24, 2010 at 6:00 am  Comments (6)  
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6 CommentsLeave a comment

  1. Awesome. My own megadungeon based on the Cave of Swallows gave me calculating fits. It has a spiraling stair and I was trying to calculate how tight the spiral would be and still have steps that were walkable by humans. Also, I needed to know how long it would take to traverse etc. I should post it someday, but I used cardboard oatmeal boxes, dental floss, and paper rolled into tubes to figure it all out.

  2. Jesus, that’s a big hole.

  3. That mine is almost 2,000 feet deep (1970 feet).

    • How many inches in a 1970 foot? I’m terrible at calculating inflation. 🙂

  4. […] They reached the third “level” and were attacked by dragonmen while Matrim was searching for secret doors.  The dragon men hurled some javelins, and then attempted to grab the PCs and carry them off.  One managed to grab the magic user and carried him up 50′.  Already injured by arrows earlier in the fight, this dragonman was slain — leaving Garmin to plunge to his death had he not used a “Web” spell to attach himself to the sheer cliff face. ( There is a drop of about 70 feet between each of the higher levels of the pit — see the table here.) […]

  5. […] an enterprising or daring party could access at almost any level, given enough rope.   I posted stuff about it earlier  (also here and here) but wanted to keep the DM tools for it a secret.  Not much need to now.  […]


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