The Implosion Mines are the ruins of an ancient dwarven civilization that mined by force rather than by pick. The dwarves of this era worked a Dynus seam that ran beneath their mountain, and they had learned to use it with a control no one has matched since. A measured pulse of force collapsed a pocket of ore-bearing rock inward, crushing it loose from the surrounding stone without bringing the roof down. The method took decades to refine and generations to master. It also, in the end, killed every dwarf who knew it.
The seam breached around 20,000 BSD. No single reckless working tore it. The dwarves had simply drawn on it too long. Each implosion took a little more force out of the seam than the seam settled back between draws, and across centuries of mining the deficit compounded, the way a well drawn faster than it fills runs dry. The seam stopped settling. Then it failed all at once. Every measured pulse the dwarves had ever spent came back out in a single moment, and an entire range folded inward onto the city in the space of a few breaths. What the breach left behind was a crater, and very little else.
The ground there has never gone back to behaving. Gravity pulls inward from every direction toward the floor of the crater, as though the breach left a permanent lean in the world that all weight now answers. A dropped stone falls sideways toward the center. Rain bends as it comes down. Stand too long on the inner slope and the pull works at your footing, patient and steady, until you are leaning into it without having decided to.
A weighted line lowered into the crater does not hang straight. It curves inward as it goes down, and below a certain depth it lies flat against the inner slope and will not come back up. Survey crews who have tried it lose the line and keep the story: that something at the bottom takes the end and holds on.
The breach left things living in the ruin, after a fashion. The miners who stood closest when the seam tore did not all simply die. The force that came loose worked into some of them and stayed, and what it made still moves through the crater. Surveyors call them the Heftbound and sort them into two kinds by which way the lodged force pushes, one driven outward and one turned inward. They are the only part of the lost city that still answers a visitor.
Most accounts hold that everyone died in the Collapse. The accounts are reasonable, since nothing should survive a mountain folding shut, and the Heftbound are the standing argument against them.
The dwarves metered the seam with one master regulator, the engine that held the whole working in balance against itself. It sat at the heart of the works, which is now the heart of the crater, under the deepest reach of the inward pull where no surveyor has ever stood. It is still down there, and it is still holding charge. Whatever keeps the crater's gravity bent the way it is bent has a source, and the source could in principle be found, broken, or made to run again.