| D20 | Adventure Hook |
| 1 | A group of local miners haven’t been heard from in days, prompting their loved ones to ask for assistance in finding them. Investigations into the mine reveal a strange sinkhole that reeks of sulfur and smoke. |
| 2 | A cult of the Devourer has claimed a section of a cave system as the site for a ritual designed to destroy the entire planet. Aboveground, a nearby town is terrified as tremors and sinkholes open in the surrounding area. |
| 3 | A geologist studying a crystalline cavern has noted unusual energy readings emitting from the minerals. Lately, the crystals have started shifting in and out of phase in a rhythm that suggests the cavern walls are breathing. |
| 4 | Multiple galactic corporations are vying for the mining rights to a rich starmetal vein recently discovered deep beneath a planet’s crust. Adventurers hired by one company to scout the area soon come into conflict with corporate interests from across the galaxy. |
| 5 | After a planetwide catastrophe, surface-dwelling inhabitants retreat underground with what supplies they can carry in a desperate search for a sustainable new home. |
| 6 | A copper dragon has recently laired near an underground town, becoming a source of ever-more-dangerous mischief. The town’s fearful inhabitants need help driving the dragon away. |
| 7 | A planar tear has led to an influx of fire elementals, threatening a nearby underground metropolis. The residents need help holding off the elemental incursion and closing the rift to the Elemental Plane of Fire. |
| 8 | Explorations into the deepest reaches of an extensive cavern system have led to the discovery of a gigantic metallic door, the composition of which scientists cannot determine. All efforts to open the door thus far have failed. |
| 9 | Unusually constant seismic activity has recently started causing extensive damage to an underground city. Xenobiologists suspect it may be due to the mysterious agitation of tunneling wyrms in the vicinity. |
| 10 | Local archaeologists have discovered ancient ruins hidden beneath the earth, and they’re eager to find adventurers willing to accompany them on an expedition. Unbeknownst to them, the ruins are anything but abandoned. |
| 11 | A local crime syndicate recently established a hideout in a nearby cave system, shaking down locals and stashing their stolen goods underground. With corrupt government and law enforcement providing no assistance, it’s up to brave outsiders to provide justice for the people. |
| 12 | Explorers inadvertently brought surface bacteria into a subterranean fungus forest, infecting the mushrooms that sustain an underground society. The town is looking for assistance in finding a way to save their crops. |
| 13 | The customs of a surface town forbid travel into a tunnel system nearby—but people in town have started to go missing, and several of the lost were reportedly last seen sleepwalking into the tunnels. |
| 14 | Pollution from surface power plants has seeped into the earth, causing toxic oozes to manifest near an underground settlement. Not only must the ooze threat be stopped, but the surface societies must be convinced to curtail their pollution to prevent the threat from returning. |
| 15 | Spelunking scouts have noticed their comm units picking up faint signals, with voices that sound almost like chanting, occasionally cutting through the static. The signals seemed to grow stronger the deeper they explored, prompting them to call for outside protection and assistance. |
| 16 | Smugglers have been using an underground tunnel network to ferry illicit goods between aboveground cities. Local governments are seeking freelancers to help track them down and put a stop to the illegal trade. |
| 17 | An underground city is hosting its first-ever extreme bouldering competition, where top athletes gather to tackle outrageous feats of climbing. The grand prize includes expensive gear and a hefty sum of cash, drawing attention from all over the system. |
| 18 | An enterprising shaitan freshly arrived from the Plane of Earth is looking to set up a gem-mining business in some nearby abandoned caverns. They seek employees and protection, though they dismiss the rumors of dangerous predators roaming the cave system. |
| 19 | A pod of dust mantas has been hunting closer and closer to a surface settlement, despite there being ample food for the creatures in their original, distant territory. The local government is hiring adventurers to investigate the reason behind the strange incursion. |
| 20 | Excavators recently discovered an ancient temple to Yaresa buried beneath old stone. The temple, seemingly abandoned long ago, contains strange machines fueled by long-forgotten magic. The temple may hold secrets to divinely inspired technology the likes of which the galaxy has never seen. |