Naz tu'Algar (more commonly referred to as the Stormhorns Volcano, and also referenced by druids as "The Mouth of World's Fire", and local humanoid populaces as the uncomplex "Dragons' Tongue Peak") is a a peak in the Stormhorns range known for its volcanic activity, although its only eruptions have been precipitated by powerful magic.
As uncovered during the Firestorm Crusade, the ruined city within the mountain was initially a Duergar trading post (with who they traded is unclear, as is the exact timeframe of this city) under its formal name. At a later point, the red dragon Astrein infiltrated their society in the guise of a trader, and somehow (given his general lack of magical talents) crafted the Ring of Mountain Fire, a magical artefact that could command the volcano's elemental spirits. Using these, he drove the Duergar out, and claimed the city with his horde of minions.
Under Astrein, the city battled extensively with the Amelthyr clan of wood elves, both altogether unnoted by the rising nation of Cormyr due to their remote locale, eventually landing in a stalemate. In 1375 DR, Astrein would suffer an ironic turn when the Fiendfire Orc clan ousted the dragon with a surprise assault, and took up their own residence in the ruins, seizing his horde as well. This would finally bring the site forth to Cormyrian eyes, as they pursued the fiend-blooded orc clan there.
The renegade noble house of Ashby would forge an alliance with the besieged orcs, seeking to use the Conflux Point within the volcano to open a gate to their masters realm, and managing to master the Ring from Astreins horde. The crusade would prove successful in ousting them, though at great cost, and the ruins lay bereft of life for awhile, the dangerous ring taken away by War Wizards and not seen again.
Remnants of Astrein's forces, joined with other humanoids pushed into the region by Shadovar, would conquer the location, aided by in their efforts by a trickle of trade with more nefarious folk from Arabel. A fleeing Phaerimm briefly hid itself amidst these tribes, but was unseated by more adventurers, exposing it as the source of various false prophets relating to the Shadovar.
Back in their own will, the hobgoblin led group of monsters continued in their (relatively) peaceable manner until the arrival of another red dragon, Zhool. Zxhool would be defeated by the arch-druid of the Ashen Glade (having caused the Ashen nature beforehand), and men of New KIlgrave, but managed to somehow trigger the dormant volcano in the midst of his demise, burying the citys entrances under lava flows.