You need to go to the Crystal Mine as told by the goddess in the bishop's dream but you can't just leave the refugees. Mine Manager Brinker is standing by the wall with one hand on the wall. Ask what is happening.
Objective: Talk to Mine Manager Brinker
The wall may collapse if Brinker releases his hands off the wall. Let's look for some rocks nearby to block the holes on the wall for Brinker.
Objective: Collect Reinforcement Stones from the rubbles nearby
Give the stones you collected to Brinker.
Objective: Give the Reinforcement Stones to Brinker