So I'm going to discuss the process by which the "dungeon" of Westmount from TMGS came into existence. To be clear, it's a small dungeon and I don't mean to suggest that it's a great dungeon worthy of any top 10 list (not close), but a lot of the thoughts from my previous few posts did come into play as I was designing it. So without further ado...
The basic steps were as follows:
1. Quest Conception - This was the step that developed the need for the dungeon and tied it to the overall game world. This step also defined the exact locale and locked in a few very basic core goals.
2. Dungeon Layout - This results from knowledge of how the dungeon came into being and should make sense given that knowledge.
3. End Boss Development - Pretty self-explanatory.
4. Dungeon Population - This comes from imagining how the current denizens use the dungeon... and how the party will find it when they enter.
5. Finishing Touches - The final step adds in some cool items or encounters that put the dungeon over-the-top.
A greater explanation of how these steps applied to the development of Westmount follows.
Step 1: Quest Conception
Westmount was pretty close to the last thing added into TMGS campaign. As I was play-testing the supposedly-finished campaign, I became wary that every side-quest was directly related to the critical path. To be clear, that was a decision I had definitely made at the beginning. I didn't want Navatranaasu to feel like a bustling metropolis with all sorts of people throwing their problems upon the PC. Rather, it was to be a small, desolate village where most of the inhabitants' problems ultimately had the surrounding Malarite cult as the culprits. (Compare this to Waterdeep, where two people hand you totally unrelated quests in just the short time you're there... but then Waterdeep is a completely different animal.)
Nevertheless, I eventually decided that it would be better if there were at least a couple optional quests and so Westmount was born. Other quests added around this time for the same reason include the Haunted Tree and the Legal Conundrum posed by the two fools in the tavern.
I knew right off the bat that a large Durlag's Tower-style dungeon wouldn't make sense given the setting; nothing that big would be near so small a town without being a large topic of conversation. So the dungeon had to be small enough to be believable within the setting.
A second desire was that I wanted all of these unrelated quests to have one thing in common with the core path: the central theme of justice, a topic near-and-dear to every Tyrran and the thread that holds the entire campaign together.
With these two goals, I began to toss around ideas for a few days. Fortunately, I was helped in this task because I had already written a detailed history of the area and so had established the previous existence of a ring of defensive fortifications built by the town's founder, Alred I, which had slowly fallen to ruins in the three to four generations thereafter. I soon seized on one of these ruined forts for a ready locale that was believable within the setting, but how would this lend itself to the central theme of justice?
The established history of the town again provided the answer. The town's past already included a series of wars against local orc tribes. I could extend this to include the notion that one of the defensive forts fell to demi-human enemies several decades before. The notion of justice came in by adding rumors of collusion between the fort commander and the invaders which led to the fort's surrender and the slaughtering of the garrison. Since that time, the family had been shunned in the town as the descendants of a traitor. Needless to say, they had tried to prove their ancestor's innocence, but none had had the adventuring skills required to investigate the ruined fort. Today, the current member of the family, Fahl Derrickson, comes to the PC asking him or her to find the proof for them.
Fortunately, the outer forts and the demi-human wars had already been written into the dialogs of several of the town's inhabitants, so everything was entirely believable within the setting. If this hadn't been the case, I would have needed to amend certain conversations or else develope an entirely knew locale unknown to the inhabitants. Fortunately, I could skip this because I had done a lot of homework with the town history up front.
So everything until now had shaped the outline of the quest. Obviously, a quest is not a dungeon, but the narrative created above would dictate how the dungeon developed.
Step 2: Laying Out the Dungeon (or Westmount, the Bad Old Days)
When mapping out the dungeon, I turned my mind to the way the fort must have been used in the past. My original concept was of a hilltop fort reminiscent of - but not an exact replica of - a motte-and-bailey from medieval Europe. The exterior map is shown below.
The hilltop fort is built on a hill with a surrounding moat (in this case without water) and an interior wall at the top of the moat. A bridge leads across the moat to a small gatehouse that serves as the fort entrance. All structures are now in a state of disrepair.
In the past, the hilltop fort would have been surrounded by small wooden buildings holding some of the more dangerous or uncomfortable functions (such as black-smithing), but these temporary buildings have since been destroyed with the wooden pieces used for other purposes. In case of an attack, a few guards could have held the gatehouse against a much larger force, but if the worst happened, the bridge could have been destroyed and the interior wall held against a much larger force.
The first floor map is shown below. Note that green boxes are meant to illustrate where doors are.
I think the notes on the picture are sufficient to explain how the fort would have once worked, so I'll refrain from further comments on that. My estimate is that there would have been three officers, including the garrison priest, and around 20 - 25 soldiers manning the fort.
The lower level map is shown below.
This is where the nasty business happened. Note that the part outlined in yellow is the portion of the map that wasn't part of the original fort. It is meant to model the point where the invaders tunneled into the fort. The passage has since collapsed and from the area that is accessible to the player, it looks as though the "tunnel" goes on for some time.
Why go through this exercise? Because examining the motives of the people who built the fort helps me determine exactly how large the dungeon should be, what the general layout should be, and what material should be in each room. For example, even if the banquet hall is no longer used as such, knowing that's what it once was helps the level designer (still me in this case) use the right placeables and effects to tell the room's story. This step starts the dungeon's story, and we'll finish it as we go.
Sometimes, of course, the builders of the dungeon will be the current inhabitants. Even so, that doesn't mean every room shouldn't have a purpose or a place. It just means this step and the fourth are pretty much the same step and can be treated as such.
So back to the example, the fort garrison was slaughtered 90+ years ago, but the demihuman mob that overran the fort has also moved on in the meantime. So the question confronting me, the dungeon designer - and eventually the player - is what's moved in since?
Step 3: The Big Bad
The big bad is an important piece of giving a dungeon it's personality. Since this dungeon was by definition separate from the core path, I had absolute freedom to create a new villain with motivation entirely separate from the Malarites. I knew that the party would consist of a single cleric and a single ranger of about 8th level at the point they would arrive, so whatever enemy I chose had to be a suitable challenge for that party structure.
I tossed several ideas around but eventually dismissed most for one reason or another. A couple of these level-appropriate options were:
1. Yuan-Ti: Navatranaasu was already established as a mountainous environment, which wouldn't fit them, and the yuan-ti had already been done extensively in SoZ.
2. Demon/Devil: Generally too powerful and most are immune to normal weapons. Since the party would only have normal weapons at this point and an encounter in which the PC would take possession of a magical weapon already formed a crucial and unchangeable part of Act III, I had to throw this group out.
3. Powerful Human/Playable-Race Demihuman: A possibility, but the campaign was already heavy on human villains (the Mistress, Eton Skye, and Dezlentyr), so I wanted to use this chance to feature non-human monsters.
In the end, I chose an ogre mage. I've always liked them for some reason - maybe it's the combination of brains and brawn - and I don't think they've been overly done in official games. I used one in SG V as a boss in the sewers beneath Tyrel's Pass and I thought that went well.
However, part of making a dungeon memorable is making its boss memorable, and part of making a boss memorable is giving it a bit of a different spin, i.e. surprise the player a bit. So I started by giving him an admittedly-slight back-story. He was supposed to be an ogre with a gift for magic that had been exiled from his society for studying the work of a now-deceased human illusionist named Melifluorius. So enamored by the work of this illusionist was he that he actually took the human's name for himself. Although the ogre mage was aware of the Malarites in the region, he was not allied with them. In fact, he had little respect for their transmutative magics and so had come to despise them. He had even come into conflict with them on rare occasion, though never seriously enough to cause one to wish to eliminate the other.
This was all I came up with, but even this slight background began to shape the boss encounter. Most obviously, it influenced the encounter dialog, which provided hints - assuming the player asked - of the ogre mage's motivations. Second, I wiped the spells of the standard ogre mage template and instead gave him spells suitable for a wizard who had studied illusion magic. Finally, I was led to a quick thought on combat tactics that would allow me to do something a little unique. I imagined that an enemy who was an illusionist would make themselves invisible once they realized their home had been entered so that they could observe the intruders from a position of safety and make a surprise attack first, if needed. I hoped all of these would keep jaded players overly-familiar with D&D and CRPG conventions just a bit on their toes and provide a slightly more memorable encounter. This was accomplished by having the ogre unleash a fireball as the encounter begins, thereby revealing his location, unless the player has already been able to unveil him and thwart his plans.
Step 4: Populating the Dungeon
The ogre mage had already been decided, but what else is there now in Westmount? To answer this question, I needed to return to the idea of dungeon ecology. What would the ogre mage permit to live there, or what could live there in spite of his wishes? Also, I needed to understand which of the already-existing rooms would be inhabited by which monsters.
I started to answer these questions by remembering that every high-level wizard needs some evil henchmen. I imagined that some lesser demihumans would have been drawn to the ogre's power and these in turn would be useful to him as workers, fetchers, and guards. Having taken the bottom level for himself, the ogre would have given his underlings free reign of the upper level. He would want his privacy, of course, and so would not want them to come to the lower level. When he needed something, he would shout his orders up at them or communicate via a projected image. After playing around with goblins and gnolls, both of which were discarded as being too weak for 8th-level adventurers, I settled on bugbears. The map below shows the upper level as it currently exists. The red box outlines the area currently inhabited by the bugbears.
The front room has become their main living area while the area once used by the soldiers as a barracks has been converted to storage and also a small shrine to one of the bugbear gods. For the most part, the bugbears only inhabit the main room and the immediate grounds outside, where they spend most of their waking hours. (Indeed, this is where the player first meets them.) The bugbears freely roam into the right-most wing of the ruins, but only rarely, as anything of interest to them has already been stripped and hoarded into their main living area. After some play-testing, I settled on five as the population that provided the most suitable difficulty level for a party of two 8th-level adventurers.
Even though the bugbears roam into the right wing of Westmount, a group of giant rats has found a way to coexist within this same area. For the most part, they stay hidden when the bugbears approach, as some of their number has ended up in the stew pot. Normally, they scavenge for food in the interior, only occasionally venturing outside through holes too small for the PC or bugbears to use. However, they are not very well-fed, and when creatures other than bugbears approach, they are liable to leap from the holes and attack.
There is one denizen of the first level that has moved into the left-most wing, and it's one the bugbears have learned to give a wide berth to. A giant black widow spider has taken up residence in the rafters above the old dining room. It lies in wait until someone ventures too far into the room, and then it descends in such a way as to cut off escape through the door and attacks with its venom. One of the bugbears has been killed earlier and so the others now fear the spider and have closed off the room. The spider, for its part, doesn't have the sentience required to fear the bugbears in the same way. It almost certainly would if it could, as the combined strength of the bugbears would overpower it, but it is content to inhabit only its small territory. For the most part, because the bugbears rarely enter the "no-man's land" between the two territories, the spider must resort to feeding on birds, snakes, and other carrion.
Those are the ecological rationales, but the selected creatures also work from a combat diversity standpoint. The bugbear group was formed into a more balanced party by including a shaman in the group of five, and the black widow's poison provides a completely different type of challenge to the party. By having the spider descend from the roof only after it can place itself between the PC and the door, the PC is put on notice that an "empty" room doesn't necessarily mean it is truly empty. The rats are a nuisance that will likely only nick the player, but they do seem to swarm the player from all sides and may serve to keep the atmosphere a bit tight.
A last comment before I move on is to note the projected dungeon flow, which I give with the green arrows. If the player picks the leftmost path from the interior, it is possible they could bypass most of the level. Since they must already confront the bugbears outside and the rats and black widow are extraneous to the main narrative of the dungeon, this is an acceptable scenario. However, as a practical matter, most players will take the opportunity to explore, even if they've already found the means of advancing forward, and so will encounter these monsters too.
The current map of the lower level is given below.
Note that even though there was once a door between the prisons and the torture chambers, I "blocked" it with a huge desk so that the flow outlined by the green arrows is forced upon the player. It's not an important detail, but it's one of many I included to show how the current inhabitants of the fort utilize it differently from the previous ones. Whereas it once made sense to have a direct path between the prisons and the torture chamber, the ogre mage prefers there to be only one path into his sanctum, and of the two paths he could have chosen, he selected the one that leads more fully through the lair of his undead guards.
Speaking of which, I decided that the ogre mage has raised a few ghouls from the remains of those who died in the prisons. These serve as his final guards as well as posing as a buffer against the bugbears in the event they decide to try to overthrow him or steal his treasure. For the most part, the ghouls roam the prison area in search of food that has long since been consumed. Hence, they are ravenous and attack anything - except their creator - that enters the room... including the bugbears. Occasionally, Melifluorious captures a creature either for his research or to torture them to learn information (he even nabbed a careless Malarite once!). When he finishes with these unfortunates, he throws their remains to the ghouls, but these snacks do little to sate their endless hunger.
The actual end fight starts with the ogre mage invisible, and he'll try to question the player to determine their reason for being there. During this dialog, the player can learn of the ogre mage's interest in illusion magic as well as his disdain for the Malarites. If they have "Detect Invisibility" memorized, they can even strip away his disguise (and avoid his initial fireball attack). Regardless of how the conversation progresses, however, Melifluorious will sense the PC's inherent power and attack.
The final room before the rockslide includes the evidence the PC has come here for and will allow the completion of the quest. (As an aside, I decided to have the evidence prove the treachery instead of disprove it, a slight twist to the quest that is outside the dungeon design.)
As far as combat goes, the entire challenge for this level comes from the boss himself. The ghouls would provide some stress to nearly any other class, especially given their stun ability, but an 8th-level priest can destroy them quickly. Hence, like the rats, the ghouls are there because the dungeon ecology demands they are, not because they pose a real challenge to the player, although they do flesh out the flavor of the dungeon. As a practical matter, the only combat encounters that will challenge the group for the whole dungeon are the bugbears, the black widow, and the ogre, and I adjusted the difficulty of these three encounters - especially the first and last - accordingly.
Step 5: The Final Touches
I wanted to add a couple neat non-combat things to Westmount as well. One of these actually necessitated itself during one of my play-throughs when I got hit by the black widow and suffered an ability score drain when my PC didn't have a restoration spell memorized. That proved a problem, so I added the option to use the old chapel within the "no-man's land" on the first floor. By cleaning up the Tyrran altar, the player can pray and relearn spells, if necessary, allowing a second full dose to handle the lower level or the learning of a restoration spell if one is required after battling the black widow.
Ever since my P&P days, I've also tried to place some unconventional treasure now and then. Again, variety is the spice of life, and gold and jewels aren't the only valuable thing out there. For example, in SG V, I had a painting in one of the manors that was exceedingly valuable, and the player could take it if they passed a lore check identifying it as a lost masterpiece. I returned to a similar idea with Westmount. The red dot in the kitchen on the right is the location of an old vintage bottle of wine that is still in good enough condition to be sold for more than many gems or necklaces would bring.
So that's a quick outline of my methodology in creating a dungeon. It's not remotely good enough to be considered a classic, but it serves its purpose, which is to provide a couple hours of fun and a memorable quest for my players.