This Classical Age God Power reduces enemy walls and towers into rubble. It will damage any shooting building, but will absolutely destroy even multiple walls in its area. The Undermine always moves towards the closest enemy wall, so target it carefully for maximum effect.

To Undermine an enemy’s defenses, left click on the Undermine icon, then left click near the walls and towers you want to attack.  Only fully upgraded walls and towers can stand up to the power of Undermine.