Dourstone Mine
The most productive of Rangolin's iron mines, and the first one he acquired in Diamond Lake.
The party learned from Filge the necromancer that Rangolin had fallen in with a dark group called the Ebon Triad, and had allowed this cult to fester in a secret chamber underneath his mine.
The party infiltrated this chamber, and found it well-garrisoned with cultists of Vecna, Erythnul, and Hextor, though the Vecnan cultists seemed more preoccupied with a creature called Kyuss than with their own deity. They were captured when a trap gave them away, and forced to retreat. They collapsed the elevator behind them, hoping that would seal the cultists within their own prison.
Architecture
The mine is cut into the side of the Cairn Hills. The bulk of its construction is subterranean, but there is a wood-and-stone guardhouse and management office outside. Dourstone's guards work in shifts here, as much to keep corporate spies and thieves out as to make sure no worker leaves early.
The mine is cut at a downward slant into the hill. One passes the barracks where miners sleep between work shifts before reaching the actual mining levels. Workers in this mine stay below for two weeks at a time, after which they are permitted to spend a week in town before the cycle repeats.
Defenses
Dourstone employs a contingent of guards both outside the mine and within. The guards outside watch the entrance twenty-four hours a day. Within the mine, Dourstone's management patrol the active areas. Their work is to make sure the miners are working, that none of them complain too loudly, and that those who collapse are moved out of the way in an efficient manner.
History
This was the first mine Dourstone acquired in Diamond Lake. His surveying process was secret, and no one quite understands why he chose this location. In the beginning, his peers claimed he chose it at random. But given the mine's production rate, it's hard to deny that it was a good choice.