Anaketsu, The Cavern of Crystals, is an incredible natural sea cave off the coast which serves the Aranami pirates well. Only accessible by boat, the walls of the cave emit an eerie ice blue light all of their own.
Most scholars ascribe this glow to the algae that clings to the marble rock, but those inside the cave swear that it is haunted. They say that the walls themselves can hold the echo of a voice for a hundred years, so none dare so much as breathe a word when they enter the cavern for fear that it will betray them long after they have gone from this place.
Those who chart the cave itself note that the interior passages are unexplained by tidal or geological pressures: whatever early humans excavated the cavern, their purposes were unknown.