The Second Founding
Thunderspire Mountain was originally home to Sarun, the grand underground labyrnth city of the Minatours. Some three hundred years ago the city decended into civil war and the population wiped itself out. In the time since then the city has become home to all manner of subterrianain monster.
About 40 years ago a group of mages devised a way to take control of the ramaining bronze warders. Massive Minatour constructs that were built during the hieght of the city. Using these warders the mages cleared out large areas of the upper labyrinth and established a bastion called the Seven Pillared Hall to trade with the various races of the underdark and explore the rest of the city. These mages came to call themselves the Mages of Sarun.
The main labyrinth is contained mainly within the mountain. Though its lower tunnels eventually lead to the upper reaches of the underdark. There is also an underground road system that leads eventually leads to the silvershield dwarven hold among other destinations.