The metal front gate was already exceptionally sturdy, capable of withstanding a nuclear attack. After completely sealing it, they piled rocks against it. Meanwhile, the rear mountain was highly secluded, easy to defend but difficult to assault. In addition, there were Transcendents in the team who employed various Magic and Artifices for concealment at the time.
Logically speaking, this refuge could be considered utterly impregnable.
Yet, they stayed in that refuge for less than five years before it was overrun by swarms of Monsters, Beasts, Curses, Spectres, and Bizarre Rules, which destroyed the refuge. Nearly half of the 20,000 people died in that catastrophe, leaving the survivors with their most harrowing memory.
Since then, they adopted a semi-nomadic lifestyle, clearing ruins, searching for new shelters, recuperating for a while, and then repeating this cycle.
