The Necromancers' Wish

From the introduction:

Each summer, the necromancer Nandoleeb leads his goblin-like Ricalu people on an underground pilgrimage, travelling by giant isopod to a sacred network of cliffside caves.

There, the very air is filled with the power of a host of ancestral necromancers. Their whispers grant Nandoleeb an unconscious, transformative power over his surroundings.

Before the scratchings and diggings of the Ricalu, the caverns were a mine system dug by the now long-dead Martoi. It is here they once sourced their rare and magical pigments. Some of their treasures remain.