Fallout Equestria: And None Shall Follow

He sat, staring at the massive steel door set resolutely into one wall of the cavern. Even as he felt the cave walls tremble slightly around him, the massive door stood, firm and unmoved by the waves of chaos gripping the world. By all that was good in the world, he hoped this was thr right thing to do. He could have opened it, could have let them in. They would have understood, he hoped. Would have understood enough at least, to leave it alone again, once it was safe, bury it, let it be forgotten. But... he couldn't trust it. It was to dangerous, what was locked on the other side of this door. This place had been built to withstand anything. Even as barefire raged across the landscape, it would stand secure. And that was the problem wasn't it? He had a safe, secure place for him and his to ride out the apocalypse, if only he was willing to risk another by letting them know just what had been hidden here.

He couldn't risk it. Better to let them all risk death outside as barefire rained from the heavens then risk letting loose what they had secured here. He had done all he could to make this place safe. The threat couldn't be destroyed, so let it sleep here, forgotten, until the mountain crumbled into dust. No one but he could open the door, and no one but he even knew it was here. Even if someone stumbled across it, they couldn't open it. It had been built to withstand a megaspell, nothing they could try would ever let them enter. Finally decided in his course, he turned his back to the door one last time, heading back up the labyrinth of tunnels, back to wear the others had taken refuge from the balefire above. He had supplies to organize and an entire towns populace taking refugee above that needed his help. They would survive this, equestria may have fallen, but they would persist. Let the door remain shut, let it pass away, unremembered and undiscovered. His only real doubt about his course was the possibility that someone, someday, would find a way inside. All he could do was pray that they would be wise enough to let what was inside remain forgotten, or, if they didn't, that Equestria, or whatever was left of it, could survive it.
....
And thus, the door was shut, and remained so. Though it did not remain forgotten, as its ceiler had feared. It was discovered, a door, sealed shut, set inside a cave, deep under a mountain. A local curiosity was soon born. A door, hidden from the world, which none could open. Many tried. As the fallout blew and glowing snow fell, those who had taken refugee tried and failed to get into what appeared to be shelter. The radiation faded, and they left the caves, but still, foals and the foolish would return, trying to breach the unopenable door. Had the small community descended from those that escaped the apocalypse in the caves not been so remote, word would have spread, and a host would have come, following what had become a legend of an unopenable door, guarding treasure beyond compare. But few would ever come to this isolated community, set out of the way in a far corner of the wasteland that was once Equestria. Thus, the door stayed shut, keeping its secrets for over 200 years, until, at last, that poor fool the ceiler of the door had briefly foreseen, opened it.