There's a diagram in "In the Cage" that shows commonly-known and used portals and their destinations. It mentions two locations that as far as I know are only mentioned there: the Public Baths in The Lady's Ward, and the Duergar Foundry in the Lower Ward. Since the Public Baths are in The Lady's Ward, who gets to use them - only the Golden Lords? Or could they be located in the Temple District, where the common people are allowed to gather? Of perhaps more interest is the Duergar Foundry - what are they making there? Weapons? (Since Duergar are evil, I presume it can't be good...)
Ideas or info on two barely-mentioned Sigil locations?
As far as armor goes, Traban's Forge also makes armor. I wouldn't assume either the Doomguard or the Godsmen have a monopoly on forging - the Lower Ward is full of smithies. The quality of Godsmen work is generally not very great, so there's plenty of room for more skilled craftsmen to manufacture higher-end items. There are other weapons shops around the Armory, too, specializing in more custom-made goods. See Sigil and Beyond, page 80 and 81.
The Transcendent Order doesn't own the only gymnasiums in the city, the Guvners aren't the only lawyers, the Sensates aren't the only courtesans, and the Xaositects aren't the only rabble. What the factions are, are powerful political organizations who also perform some useful function in order to keep on the Lady's good side.
As for duergar, I'd want to add some "Planescape twist" to them. Maybe they don't forge metal, but some more exotic substance like ectoplasm or flesh (with an emphasis on the psionic nature of duergar). Maybe they're refugees from Laduguer's realm who have taken up the worship of Moradin or Ioun or Ilsensine or Io or Diinkarazan or Xan Yae or the githyanki lich-queen. Maybe they're simultaneously rivals and friends with Traban and his family, with a friendly antagonism that goes back many decades. Maybe they have close ties with a kobold community or the kaorti or the zern.
The Doomguard's Armory probably controls what are typically considered the city's weapons and armor; the materials used to equip a hastily-drafted fighting force bigger than the Harmonium can quickly field, major riot gear, or siege engines used when a significant physical threat develops within the city. Likewise, it probably holds moderately powerful magical paraphernalia that the Harmonium, Doomguard and armed wings of other governmental entities (hey, the Fated have to have some protection from the nastier tax cheats) pull out when there is a more serious threat, but aren't trusted with on a regular basis.
The Armory doesn't actually make weapons and armor, apparently; it just stores them. In the Cage talks about the weaponsmiths and armorers that have set up shop near the Armory. So the duergar foundry is probably exactly that -- a place to get dwarven metalwork, if one doesn't mind dealing with the duergar -- or needs duergar work specifically for some reason.
The Armory does forge weapons, actually. See The Factol's Manifesto, page 42.
"Billowing up from the center of the Armory at all hours of the day or night is a tremendous blast of heat and light from the huge weapons forge below... The mighty weapons forge takes up the center of the floor... Those looking to have a special-order weapon made can talk to Cromlich at the central forge. A weapon fired in the forge costs three times the standard price, but they're exceptionally well made and worth every coin."
Apparently just weapons, though. No mention of armor.
That doesn't mean that the Armory doesn't also store weapons that it doesn't make.
They could be duergar from Golarion - on that world, they are corrupted dwarves that have allowed their craftsmanship to fall into extreme mediocrity.
This forge would then produce vast quantities of substandard metalwork, although it would still be of interest to sages of dwarven society.
Pants of the North!
I like the idea of a weapon shop so terrible that they don't even pretend that warriors are their target market, marketing instead to scholars of shoddy weaponry throughout the multiverse. "You simply must visit the duergar forge in Sigil, professor. I wrote three books on the way their handles snap apart when you grip them with more than three fingers, and had a well-received paper in the Journal of Critical Fumbles on how their blades fall on your foot if you swing them too hard. The place is an absolute goldmine. A truly fascinating culture."
I would go the mythical root and say they craft things like silk strong enough to tie up wolf gods and wooden rings that ensnare people's minds.
Oh, but for a psionic bent, maybe the greatest of them can smelt knowledge into people's heads and reforge broken minds!
I would pacifically say nothing in the foundry is metal.
~
Public Baths is less interesting to me, however I'd say it was run by nymphs or some sort of creature that can keep the place clean.
I particularly like the idea of the duegar having a psionic forge. The creation of psionically enhanced or empowered items seems like something that would have a market in Sigil (and elsewhere) and it is also unique enough that it would be difficult for other forges in the city to make inroads into that market.
This made me think of the idea that their is a psionic Cold War playing out in the streets of Sigil. Since it doesn't involve physical combat or showy magic (most of the time), there could be a lot of unexplained phenomenons occuring with select covert agents striking psionically against other agents.
E.g. a weaponsmith popular with the PCs (who was trying to forge a psionic item) suddenly flails in agony and then drops dead.
Later a quiet scholar of a different faction goes stark raving mad (the scholar was the actual psionicist that was working with the non-psionic weaponsmith - but he lost a mental battle with a duegar psionic enforcer)
Agents from one or more camps could be trying to subtly gain a superior posiition while sending a large number of new barmies to the Gatehouse.
Imagine all the possible false leads the PCs could run down before they get a clue as to what is really going on. And imagine the damage that could befall the PCs before they are aware/prepared for what they are up against.
The PCs might have to turn to a neutral party knowledgable in psionics in order to protect themselves. Would the PCs feel comfortable dealing with a "neutral" mind flayer if it meant they could attain their goal?
Good questions:
Personally, I'd say the baths are open to whomever can afford them. Or perhaps there is a cheap area of "common" baths (to make enough money to sustain the operation) and a more lavish and expensive sauna experience for those that can afford it. (I could see a lot of secret deals between high-ups being worked out in these private baths)
The Duegar Foundry poses a more interesting question to me.
If the Doomguard control the Armory (for weapons and armor) and the Godsmen have the Great Foundry (for mundane items), what's left?
I had always viewed the faction businesses as monopolies (or at least virtual monopolies) what would the duegar make that wasn't the domain of another?
Or are they a rare example of a business that somehow resists the monopoly? If so, I imagine that the faction that overlaps (let's say the Doomguard) would NEVER shop there and the foes of the Doomguard would shop there covertly.
Of course, the duegar MIGHT be members of the Doomguard just working on some specialize type of equipment.
Or it might just be a leftover name - i.e. the duegar USED TO run a foundry there; but it was taken over/shut down/building converted to something else - but it still retained its prior name