The Pathfinder Megadungeon

You've been down underground for days. 

When your party's thief said she smelled some gold down that dark corridor, you said it was a bad idea. You were low on food, water, and light already, and your pockets were already almost full with what treasure you could carry. Why test your luck any further? Why tempt fate?

The rest of the party decided to go along, though. Instead of treasure, you found a pit that deposited you all three floors deeper. Without a map showing the way out, running and hiding from the monsters that stalk its corridors, you've been out of food for days, and the waterskins are down to their last dregs. 

Then, from around the corner, voices. Orcs, lesser servitors of the minotaur king that rules this level. Your party sets upon them from surprise, and loots the bodies. Flasks of lamp oil, good. Food, better. Water, best. And maybe, just maybe, this crudely-scratched piece of tree bark is a map. 

It's a playstyle that might feel weird and alien to lots of gamers today, but that kind of scenario, in which the challenge of a dungeon is not just to clear it, but to survive it, goes back to the earliest days of adventure gaming. It's a fantasy that leans less on heroic action, and more on a kind of survival horror. You want to change your fate and become something more, and for that you need magic and gold. There's gold in the dungeon. But there's monsters in the dungeon, creatures that will drag you into the dark and eat you if you aren't careful. If you want to fight those, you need equipment and power. Magic and gold would be great for that. Where can I get some of that? Oh. 

This was a style of play exemplified by the megadungeon: an adventure site that was not meant to be cleared out in a single expedition, or even a handful, but which you could keep coming back to again and again, growing ever more powerful and going ever deeper. Dozens of levels, hundreds of rooms, with monsters that repopulate and move between delves, so large that it can never be fully cleared. 

As the fantasy adventure game met new audiences and changed, that survival horror aspect got outcompeted by heroic fantasy, largely centered around combat, with lots of character customization. That's how you start with game where character creation is two choices, six numbers, and some equipment, in which combat is much more zoomed out, and fifty years later wind up with Pathfinder 2nd edition, in which your character is developing constantly as you level and highly detailed combat is the core of the game. 

But despite that change in the major systems and assumptions of play, the appeal of the megadungeon has never really gone away. Though they went out of fashion for a while, people never really stopped publishing them, and the standards for sheer size seem to just keep increasing, from the ~1500 rooms of Stonehell to the over 2000 rooms in the Halls of Arden Vul. Outside of old-school and indie publishing, megadungeons came back into the limelight with an official megadungeon for 5e, Dungeon of the Mad Mage, in 2018, and the Abomination Vaults adventure path for Pathfinder 2nd edition. 

Since I'm in the process of switching my home game from AD&D 1st edition to Pathfinder 2e, at least for the coming year, I have something of an interest in exactly what makes a megadungeon and how one might work in newer systems. 

But there's more to a megadungeon than just putting a lot of rooms together. In particular, the feel of the megadungeon, the sense of exploring something vast which you might never be able to fully map, of planning expeditions, of possibly getting lost and needing to survive instead of win, is something which arises from the interaction between the rules of the system and the form of the megadungeon.

This is a sense which implementations of the megadungeon in more modern systems don't capture. Since I've been playing it with my little cousin lately, I'll use PF2e's Abomination Vaults as the core example, using the lens of rules+form to explore the differences and how one might create this same feeling in modern systems. 

Rules

First, what kind of rules assumptions am I talking about?

Looking at AD&D, we can see several elements which come together to create an adventure focused on exploration and survival, namely:

• Logistical Limitations: essentials such as food and water are heavy, carrying capacity is limited, light sources are similarly heavy and limited. Cleric spells (light, create water, purify food and water, create food) can pick up some of the slack, but only in a limited capacity at lower levels. A 1st-level cleric's light spell lasts only 10 minutes longer than a torch, and is competing with cure light wounds and detect evil in spell preparation. If your cleric dies, you'd best have enough of these supplies in hard form to get out of the dungeon...
• Pressure: mainly from random encounters in both the dungeon and the wilderness (with the latter often being deadlier!), combined with a very low rate of natural healing (1hp/night of rest) drives players to get as much as possible done in as little time before returning to the safety of the town. Resting in the dungeon, when possible at all, is hazardous. 
• XP Source: gold for xp encourages players to seek out treasures, following treasure maps and rumors, in order to get a smuch treasure with as little combat as possible. While combat does award XP, it's more of a consolation prize, not enough to motivate the players to seek fights on their own. 

Contrast with Pathfinder 2e:

• Logistical Limitations: While characters are limited in terms of how much Bulk they can carry, the limits on food/water and light are negligible. With 1 week's rations being a Light bulk item, a player can carry 70 days of food in a single Bulk slot (I assure you, 70 days' worth of food does not weight 5-10 pounds!). A day's water is likewise a Light bulk item, as is a torch (still lasting 1 hour, but costing only 1cp), but the real kicker is light: the light spell is a cantrip, whose effect lasts an entire day, can be recast at will, and sheds the same light as a torch. 
• Pressure: is effectively nonexistent by design. The rulebook seems to contain no guidance as to random encounters in the dungeon, and only very brief mention of them in the context of wilderness exploration. Abomination Vaults mentions the possibility briefly, but doesn't provide a mechanical framework for this, instead making it one more plate that an ambitious GM can try to keep spinning, but not part of the core experience. In the absence of an actual random encounter rate as opposed to GM fiat, these encounters lose their value in providing pressure, doubly so because combats aren't really a source of pressure in PF2e. The game is balanced such that the results of most combats are generally predictable, so unless you fill your encounter table with a bunch of severe and deadly encounters, it's going to add time to your session without adding tension. On top of that, hit points in PF2e comes back very easily, and the game assumes players enter each combat with full or nearly full hp. 
• XP Source: XP comes primarily from combat, with overcoming a trap provides 1/5th as much XP as a combat of the same level, and awards for completing objectives making up a similar minority. Players are actively incentivized to fight, rather than to avoid unnecessary fights and pick their battles. 

The result is pretty clear from the design of Abomination Vaults: while it is widely acknowledged as a difficult adventure, specifically in the combats it presents, it is still an adventure in which going room by room through each level and clearing it is the intended mode of play (it does mention in a sidebar that you should keep the dungeon active by having different monsters move in, but this has no mechanical support and thus is clearly not a design priority. Plus the big bads of the various levels clearly aren't going to respawn). 

Form

Now let's examine the form of the megadungeon and how it interfaces with the rules assumptions earlier:

First, a megadungeon's size just plain means it takes a while to cover ground, especially if you want to move slowly enough to map it out and search for traps. Every hour is another torch gone, a few more chances to get ambushed by something nasty, a little bit closer to running out of food and water. 

Every intersection is a choice: explore on, hoping you find some reward, or turn back to safety, not risking what you've already found. Caution vs greed. Some elements from earlier dungeons, which never really caught on, add a chance of getting lost or even getting dropped into a lower level of the dungeon, forcing you to look for a way out. 

At the same time, the reactivity and repopulation of the megadungeon, means that you probably aren't going to clear a whole floor, let alone the entire thing, so in each delve you must to bypass dangers you already know are there but couldn't clear out entirely, in order to get to the deeper floors where the good loot is. 

In PF2e these don't really hold. Food, water, and light are much easier to come by and weigh or cost little, treasure isn't difficult to remove from the dungeon once you've acquired it, and even a low-level PC can easily carry much more than they can expect to need. In a dungeon filled with level-appropriate encounters, there's not as much reason to be cautious, especially when fighting is the best way to reach the next level. There's no incentive to skip a floor, trying to get better loot and risking more difficult challenges: the risk and the reward are the same thing. 

And, lip service to restocking aside, the dungeon is clearable, it's just a matter of how many times you need to return to town to do it. If that wasn't the case, you could very easily end up with parties sticking around at a given floor, farming trivial encounters until they stop being worthwhile, and only then going down to what are now easy fights. This may also be why Abomination Vaults introduces milestone leveling instead of the default combat xp, to keep the players going deeper. 

Rampant Speculation

Does this mean you can't have that kind of megadungeon experience in PF2e? I don't think so, but it does men you need to rethink the form of the megadungeon, since the rules have changed as well, in order to recapture that experience. 

In particular, you would need to create new sources of time pressure and threat pressure. Just adding more wandering monsters doesn't work for the reasons listed above: combat is the reward, attrition of hit points is quickly remedied, and attrition of survival resources like food and light doesn't really come up. 

It might be heavy-handed, but my mind goes to a dungeon which is only 'open' for a limited time. Whether it's a magic portal that only opens when the stars align (the 'secret realm' trope from cultivation fantasy could be a reference) or just a physical door in a mountainside that opens and closes on a more-or-less predictable interval, the PCs are on the clock: get in, find treasure, fight monsters, accomplish objectives, and then... well, the door is going to close in an hour, and it'll probably take you forty minutes you get back. Do you push your luck, explore just one more room? Or do you hightail it back?

You'd need to calibrate this a bit, but so long as the PCs can get a lot done (but not everything they want), you push them to map and learn the layout of the dungeon so they can get to places quicker, make it less viable to take on every encounter they come across, and encourage them to make their own priorities and think in terms of expeditions, instead of just moving from room to room and knowing that their character sheets will carry the day. 

And if they get stuck inside... well, they should have plenty of supplies stocked up, right? Maybe they took the time to prepare a hidey-hole in advance, or they were able to find some kind of friendly sanctuary in the dungeon... or something that only looks like a friendly sanctuary. That's when the map is going to come in handy. Frankly, giving the opening and closing time some unpredictable variance, as little as ±1d6*10 minutes, could be great at creating situations like these and make the players nice and paranoid. 

That's not a bad thing, by the way. A paranoid party is an engaged party. So long as they have space to relax and prepare during downtime and they're greedy enough that they paranoia isn't all-encompassing, it's a great place for the players to be emotionally. 

Also, if they can't go to the dungeon anytime they please, this creates a framework for downtime activities 'what will I do until the dungeon opens again?' which gives more significance to the rules for earning income and crafting. It also makes the idea of rival parties and other factions trying to explore or exploit the dungeon more feasible, especially if you get multiple people camping at the entrance waiting for it to open, a wonderful opportunity to make colorful NPC parties and have lots of inter-party drama. 

Rules Changes

In addition to using the built in Proficiency Without Level rules to make the power curve flatter, you may also consider certain rules changes:

Logistics

1 day's water should weight 1 bulk

1 week's rations should weigh 1 bulk

Healing

Treat Wounds: takes 1 hour and can be performed every 6 hours, instead of 10 minutes/1 hour

Continual Treatment can be performed once per hour

The Battle Medicine feats and the Legendary Medic feat remain unchanged. Healing from a night's rest remains unchanged. 

Random Encounters

Make random encounters in the dungeon part of the core. Provisionally, a 1 in 6 chance of an encounter every 10 minutes with a table containing something like this distribution of encounter threat:

1: Trivial (or non-combat)

2: Trivial (or non-combat)

3: Trivial (or non-combat)

4: Low

5: Low

6: Low

7: Low

8: Moderate

9: Moderate

10: Severe

You may also consider placing hazards on the random encounter tables, though these would have to be hazards that could feasibly appear anywhere in a given dungeon level/area (and could feasibly not trigger or be detected the first time the party moves through it). I like how PF2e's hazards have unified statblocks like creatures do, but the standard ones presented in the book don't often grab my attention as centerpieces of whole encounters on their own. 

Having some random encounters be combinations of creatures and hazards could also work. 

The aspect I'm not sure how to address is light. We could make torches more expensive and remove the light cantrip, but that feels hacky. Given how many PCs already have low-light or darkvision already, it may be better to leave this part as is and instead make this a factor in random encounters. Maybe having a light active makes more dangerous encounters more likely? Or perhaps we take a page out of AD&D and have the presence of light influence the starting point of combat encounters. 

Finally, you might consider making the Refocus action take 1 hour instead of 10 minutes as well. 

Movement Speed

PF2e does actually have rules for how far you can move in a dungeon, as well as the exploration activities you can perform while doing so. However, the movement speed is quite fast, basically assuming the party's speed in the dungeon is the same walking speed as when they are traveling in the wilderness. 

This can be fixed pretty easily by reducing speed in the dungeon. A 10-fold decrease would get you to 200 feet (40 5-foot squares) per 10-minute turn, about double what an AD&D party could expect, but probably still in a reasonable range. This will affect how large you choose to make your dungeon maps. 

Treasure XP

The biggest overhaul, and possibly the most important, would be reinstating xp for gold. On the one hand, this would be relatively easy to implement, since PF2e has a working economy in which gold can buy all sorts of items and services, along with guidelines as to how much treasure, in cash and equipment, a party should earn by each level. 

On the other hand, Pathfinder 2e's economy actually values the gold piece quite highly, and it takes 1000 gold pieces to make a single Bulk. A single PC can hold the party's entire cash earnings in a single Bulk slot until 8th level. As a result, the weight of cash is not going to be a logistical limitation like it is in AD&D. 

You could choose to drop this element, or try reintroducing it, perhaps by making 1 Bulk equal to 100 gold pieces instead of 1000. Alternately, you may choose to make your treasure heavier, but this can come across as contrived. Or you may just choose to award your cash in copper and silver most of the time. 

Dungeon Design

Some further considerations about building a dungeon for this style:

You may consider making a dungeon whose deepest levels cannot be accessed so quickly

You may consider making dungeons sparse rather than dense. Stonehell, for example, is a very dense megadungeon, the entire things is pretty much contiguous. For our purposes, something a bit more like Rappan Athuk, with individual dungeon areas separated by longer passages which are not mapped out in detail. If they're big enough, you can combine this with the fact the dungeon opens and closes. Make the deeper levels, or a level containing something very desirable or strange, far enough from the entrance that the PCs will have to stay in the dungeon while it is closed: this can be a phase shift in the course of a megadungeon campaign. I seem to recall Dungeon Moon had an approach like this. 

I also quite like the teleportation nexus in Abomination Vaults. That dungeon isn't big enough, in spatial terms, to really merit a network of teleporters, but we can extend the concept: let players find a teleporter nexus in the early levels, and then need to reactivate the portals, each of which is located well into their respective levels. For bonus points, make the unopened portals unstable rather than just boringly inactive, so they can occasionally find a portal whose other side they've never located is open, and they have the choice of going in to see what's on the other side and possibly get in way over their heads. Even better if, occasionally, creatures from the other side can come into the nexus...

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