An ancient fortress deep in the jungles, visible above the canopy, a landmark that sailors use for navigation even as they avoid approaching. The Tower of Gwyndar sits at the intersection of Dark and Void leylines, a nexus of shadow and emptiness that predates memory.
The tower is black stone, seamless, with no visible mortar or joints. The architecture is wrong: doorways too tall, stairs with uneven risings, rooms that seem larger inside than outside. Whoever built it wasn't human-sized, and they weren't thinking in human ways. The Tuktuk found it when they settled these islands; they didn't build it. No one knows who did.
The leyline intersection creates absence. Within the tower, shadows are deeper than they should be. Sounds don't carry. Memories fade. Visitors who stay too long find themselves forgetting why they came, what they were looking for, who they are.
The Nkoko village considers themselves guardians, but "guardian" means keeping things from coming out. They don't enter except in dire need, and those who do enter don't always return unchanged. Expeditions from outside occasionally try to explore; the Tuktuk warn them once, then let the tower handle the problem.