Miner Control | Luculla Forest / Hiberheim - Main quests Divinity: OS Guide

After you enter the mine in the forest and see the undead miners, find a spot where you can cut through the wall with the sword (close to the entrance) and you should soon see the cultists guarding a totem. You can convince them that you are on their side but, a battle will probably ensue even though, because you need to destroy the totem.

The Totem to destroy

After you destroy the totem, return to the mine entrance and talk to the undead. In exchange for freeing them, they give you a password to the temple entrance: "Sadakandras", which you need for the "Investigating the Mines" quest. The temple entrance is in the mines, to the East.