Wiping out the Thalmor presence in town was easy, but correspondence in their barracks revealed they were actually after someone named Valgus Ponius - and believed him to be hiding out in a nearby mine. Sure enough, there were lots more Thalmor to be found within.
My place is grinding your face into the dirt, elf scum.
The high guards were particularly tough since the tunnels didn't afford me much room to back stab them, but not tough enough to outlast all my potions. In the deeper level of the mines (and boy was it a deep mine), the Thalmor gave way to bandits who were more plentiful but less tough and far less skilled. I mean, some even just killed themselves.
Soon enough I found Valgus Ponius, the crazy man leading all the bandits - thinking this mine was his castle. There was evidence his own people were going to slay him soon anyway to appease the Thalmor. Pity that they all had to die, but none of them really surrendered. Eventually, the mine was clear of all hostiles. And by all hostiles, I mean pretty much all life.