Evidently, the wave hadn’t been triggered in nearly four decades, so a complicated bit of magic would be required to access the entrance, now that it was compromised. In gruff voices, the two officers explained their process to send a rescue group to the entrance that the four visitors had arrived through. After the wave was triggered, a stone would magically block the entrance to the tunnel system, effectively trapping anyone else inside the outer cavern, magic rendered completely useless by the copper lining. (Draco looked quite satisfied at this point, for he had suspected that the copper was purposeful).