Dance of the Goblins (New expanded third edition)

They say that the earth shifts on its axis every 200,000 years. . . When the planet shifted, most of the surface dwellers were destroyed. The few pockets of survivors were left without technology and little supplies, but they built a simple feudal society on the rubble of the city. Meanwhile the creatures in the deep places moved closer to the surface, taking over the old underground transport tunnels abandoned by the humans. Their own Shamanic way of life had survived only by staying out of sight of the humans who habitually killed what they did not understand. Five generations of humans passed and the descendants of survivors settled into a way of life that was simple but satisfying, until one day a man wandered into one of the old tunnels. . .