Just found the second Infested Mine so far... and its a cluster. A single doorway opened beyond the initial area and behind it is a Seeker Soldier, about 10 Seekers plus a one star and oh about two dozen ticks with several star ones among them... Ok thanks to a spiral staircase and Bonemass power I managed to murder my way through all that, barely surviving.
My reward? A big room with almost no extra open pathways but a spiral staircase in the middle downwards that leads to at least another 4 seekers that finally manage to kill me. meaning there were beyond 30 already aggro'd mobs behind a single set of boards.
That's a bit much don't you think?