Click image to download this free multi-level TTRPG battlemap of a Bandits Underdark Crystal Cavern, then keep scrolling for the detailed adventure prompt written for it.
Deep dwarves have paid you to find trade boats that have gone missing in the nearby area, along a stretch of river that’s usually safe. There are only peaceful settlements nearby, but the two search and recovery teams sent out have disappeared as well. Now the dwarves are worried something’s gone terribly wrong, and need you to figure out what.
When you search the area where people have been disappearing you’ll find a tunnel that’s not marked on any map. It looks like it’s only recently been cleared of rubble leftover from some kind of collapse. If you follow it, you’ll come to an open cavern with an old fortress, as well as part of the river running through it.
Should you enter, you’ll find some grey dwarves, the missing traders, as well as the search parties that disappeared. They’re all quietly tending to the dark purple crystals growing off the walls and pathways throughout the cavern. If you approach, you’ll notice those same crystals growing out of their skin, along their limbs and faces. Should they see you, they will attack in unnerving unison and attempt to plant crystals into you.
WHAT’S HAPPENING? This cavern was closed off hundreds of years ago, and for good reason. The crystals within it are the remnants of an ancient, extinct race who created them to contain their minds and memories, in order to survive a great disaster.
Many of the crystals were damaged during the calamity that wiped out their creators, however. They have been growing slowly over the thousands of years to make up for what was lost, gradually restoring corrupted memories and information. But the destruction of the crystals from infrequent earthquakes is happening faster than their growth, and if things remain the same the crystals will all be destroyed.
Though they can grow anywhere, they grow unbelievably fast in organic life—preferably sentient, as they can meld with the consciousness of the creature they take over and increase their ability to think sooner.
After being locked away in darkness for hundreds of years by the ones who built the fort—for it was then the crystals discovered the use of the flesh—the crystals became despairing. It was their most desperate hour before a group of grey dwarf bandits unsealed the cavern and made camp here. Frantic to rebuild and regain what was lost, they seized the opportunity to take over their bodies—as well as those who ventured nearby.
If you make it to the throne room, you will find the leader of the grey dwarves, who is almost completely encased by a thin film of crystals on the surface of his skin, though they are growing all throughout his body. He is the most developed among the infected organics, and speaks for the hive mind crystals. Some other, less-developed organics are there in the room with him, and their leader will request to parlay with you.
He will explain the history of the crystal and what’s happening. With this information, he also offers you the choice to help him revive his civilization. This would require hundreds more sentient bodies, but he has read from the memories of those he has incorporated that dark elves are an unloved, evil race and suggests them as candidates.
In return for your help, he will offer the ancient knowledge his civilisation held—but he can only share it when the crystals have developed enough to have repaired the holes in the prehistoric memories.
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