Halruaa

The Mine

Halruaa, also known as the Mine, is the biggest open-sky mine in all of Faerûn. It is currently under lockdown, due to having been dug partly into the Underdark. Waves of monsters continously try to evade the mine and need to be contained by magic users at all times.

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Baseline information in regards to Halruaa can be found here.

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Modifications to the actual lore include:
622 after the Great War:

Beginning of the mining operations of the Halruaa's rock, under the keen eye and constant supervision of an elite team of dwarf miners. The mine is initially supposed to be in place to harvest iron, but the mining company soon realizes that the mountain is richer in resources than they initially thought.

1080 after the Great War:

The mountain that once was is no more, having been replaced with a large gaping hole. Rarer and rarer minerals keep being discovered every few decades, as the teams of diggers keep exploring the earth.

1236 after the Great War:

A new metal is discovered. It is named Electrum by the savant Vilos Santí and is expected, due to its properties, to become a new currency that would offer people more flexibility in their purchases.

1245 after the Great War:

Smelting of Electrum Pieces starts locally.

1247 after the Great War:

While digging, miners find strange looking ''tentacle-squid-folks'' that flee as soon as they are approached.

Some workers eventually start sporadically disappearing, but the mining company deems that the digging must continue in order to be able to inject the Electrum Pieces^TM into the world.

Later that year, an army of various monsters, whose existence was still mostly undiscovered to the scholars of Halruaa, attacks the miners. The attack is the first of many, and countless victims perish.

Eventually, the mine is sealed shut and Project Electrum Pieces^TM gets canceled. The information regarding the existence of this new metal is put to silence and the pieces secretly shipped to an unknown island.

As the hole is sealed, peace comes back to Halruaa. The following years are an economical disaster, as the region's main source of economy has been disabled.

1375 after the Great War:

The attacks from the Underdark restart once more, as a hole is blasted open where it was last sealed over 100 years prior. Hordes of monsters invade the neighboring towns.

Mages from all around the region rally and work tirelessly toward pushing back the invasion.

Echoes of a religious chant to Torog can be heard from the bottom of the mine.

1392 after the Great War:

The invasion is pushed back and is now at a stalemate around the mine, where endless waves of monsters come crashing against the protective spells of the mages of Halruaa.

1400s after the Great War:

Elminster, often considered the greatest mage to ever walk Faerûn, oversees large parts of the organization of the mages who work permanently around the mines. He uses a scry spell at least once a day to keep tabs on any ''overflow'' of creatures that could happen. He also finds young talented mages to provide a larger rotation of mages, to the point where most mages only have to come about a day every 2 years to lend their help.

1495 after the Great War: 

A group of adventurers called the Golden Company  enters the mine, thanks to the help of a local mage. The group delves for a while in the vast underdark tunnels and eventually find a colony of illithids led by a very powerful Elder Brain that was connected to the majority of the underdark through a near-infinite number of veins. It was discovered, after the Elder Brain was heroically slain, that it was the source of the massive unrest that had been plaguing most of the underdark for the last century.

A map of Halruaa