An Old Tree

The Elder Oak, a sentient tree that acts as the guardian of the forest, has begun to weep black ichor. The local druids are baffled. The party must shrink down to the size of insects (via a provided potion) to enter the tree's bark and clear out a parasitic infestation of gloom-beetles eating the tree's heart. Inside, the geography is a vertical wooden dungeon where gravity is disorienting.