Greywater Fastness was one of the Seeds of Hope built in the Greywater Reach in Ghyran through the Festermere Realmgate. It's a towering stronghold of ironclad walls, roaring furnaces, sorcerous wards and lowering cannon batteries. The city is built upon a vast reserve of Ghyran realmstone that is used to power the growth of the city. 
Currently, it is a city that never sleeps, its industry unhalting. To this day Alarielle is still trying to retake the city's grounds via raining fast-growing plants that require fast removal. Its streets are described as narrow rivulets of stone and metal, remnants of a tireless, ever-expanding industry. These streets widen as they approach the great canals that connect the city with its surrounding marshes. 
This city was only possible after Valius Maliti made the intuitive leap of using realmstone as a power source and his genius combined with the wisdom of the aelven enchanters, and the pragmatic skill of the Ironweld engineers the harnessing of Ghyranite realmstone began with arcane machinery. Suddenly a collective of artisans and labourers poured through the Festermere Realmgate into Greywater Reach with the protection of the Anvils of the Heldenhammer, the Eldritch Council and regiments of Freeguilds, especially those of the Greycap gun companies. The bog-grot tribes that had harassed their stockades were driven back by crackling war machines, the swamp waters were drained in days and the land was baked into hardened clay. Walls and towers increased in size as the region's resources were plundered to build the fast growth of the city. The horrified Sylvaneth even came to blows with their allies as trees were felled by hundreds to fuel the growth of the city. [4a]
During the Season of War, hordes of beastmen threatened to tear the city down and the guildmasters ordered a full salvo from its macro-Hurricanum arrays creating an arcane detonation that not only utterly wiped out the besiegers, but also turned the surrounding verdant landscape into a desolate, smog-choked wasteland. The Dreadwood Sylvaneth led by the Treelord Pale Oak move to occupy the devastated territory now known as the Ghoul Mere and refused to allow people passage out of the city. In the aftermath of another bloody conflict, negotiations are held and the city secured a single trade route out of the Fastness which becomes a militarized highway and those who stray from this path are taken away by woodland spirits.[5a]
Though the Free City of Greywater Fastness is nominally governed by a Grand Conclave, it is the lords and clan chiefs that make up the Council of the Forge who hold the most authority and influence over the city's policies. The council is driven by the desire for more resources to power their experimental war machines and seeks any excuse to make war upon Greywater’s neighbours. [5b]
Once, like nearly all Cities of Sigmar in Ghyran, a Lord Cultivator was included on the Conclave of the city. This ended when the city's last Lord Cultivator was banished, due to the belief they were working with the city's Sylvaneth enemies.[8a]
The main force that drives the expansion of Greywater Fastness is war. The high demand for Greywater weapons and refined firepower keeps wealth flowing to the Ironweld guildmasters and Dispossessed mason-lords and keeps the fires of the gun foundries ever blazing. The duardin clans that operate some of the most prosperous forge complexes have even become wealthy and powerful enough to earn a position on the Council of the Forge. [5b]
Greywater Fastness is a highly advanced location, with clockwork automatons used for common (if well to do) transportation. These are known as rattletraps, a steel-rimmed carriage pulled by a steam-powered automaton wrought crudely in the shape of a horse.
The standard doctrine for the generals of the city is the decisive application of overwhelming and often extravagantly excessive. firepower. Elite regiments of Freeguild Handgunners known as Greycaps for their distinctive headgear joins with veteran shieldbands of Dispossessed Ironbreakers and Irondrakes. Relentlessly drilled, these troops form a nearly impervious battle line. The infantry are backed up by the might of the Ironweld Arsenal with cannon and Helblaster Volley Gun batteries with bomber squadrons flanked by whirring Gyrocopters.[5b]
- Cathedral Hill 
- Old Fen Gate: The first gate built over one of the largest and oldest of the canals and it used to mark the end of the city. The walls expanded long ago and it became a haven for criminals. 
- Mere Keep: A powerful fortress gateway, constructed by duardin stonemasons of heavy black stone dredged from the marshland., it has a dozen heavy portcullises and batteries of cannon. The walls and gun towers stretch out on either side of the might gatehouse and loop back towards the road to the city. It has stables, animal pens and a forge and is as self-sufficient as possible. [6a]
Greywater Fastness has a robust population well within the millions, representing a myriad of different races.[6a] Those descended from the first Azyrite Settlers who established the Greywater Fastness and the Swamp-Cantons of Greywater Reach are known as Star-Bloods, whereas those peoples native to Ghyran are known as Jade-Bloods.[6b] Whilst slavery is illegal, prisoners are often formed into work-gangs, sent elsewhere on to the smaller settlements in the Mire, some are used to form penal regiments or press-ganged into crewing ships. [6b]
- Palem Bok: Bookseller and spy for Queen Neferata in Greywater Fastness. Intervened successfully in the Auction of Blood and acquired Charu, the Soul-Lash.
- Casper Guno: well known and feared Crime boss. [6b]
- Shayl: Aelf and former security guard of the Old Fen Gate's illegal underground, the Magpie's Nest. Currently in Pallen Bok's service.
Flora and Fauna
- Fellwater Troggoths: These haul themselves out of the filthy canals, their flabby, scaled flesh encrusted with barnacles of ossified filth and rampage through the slums, attacking anyone foolish enough not to seek shelter.
Ironweld Cog Sigil of Greywater Fastness
- 1: Season of War gaming aid from the WH AoS app, A New Power.
- 2: Auction of Blood by Josh Reynolds
- 3: Greywater Fastness product listing
- 4: Age of Sigmar: Core Book (2nd Edition)
- 4a: The Seeds of Hope, pg. 54-55
- 5: Battletome: Cities of Sigmar (2019)
- 6: Dark Harvest (novel)
- 7: Soulbound Core Rulebook
- 7a: The Mortal Realms
- 8: Age of Sigmar: Core Book (3rd Edition)
- 8a: Hammerhal Ghyra, Pg. 98-99