Black Sapphire

To most, a black sapphire is simply a rare and beautiful gemstone - a sapphire with a high enough iron content to make the stone appear black and opaque. Most commonly produced in the Iron Hills, the dark stones are not particularly valuable, and are commonly worn among the nobility as a sign of mourning.
However, the Night Watch have another use for these stones. Particularly dark black sapphires (those that are truly black, not simply very dark blue) can hold an enchantment that allows an enclosed area to be shrouded from all light. These areas, which the Night Watch call sanctuaries, can block out even magical sight, making them impossible to navigate without relying upon hearing or touch.
The Night Watch have slowly been working on a much larger ritual. The enchantment is designed to resonate with other stones positioned in the proper geometric pattern around them. In each sanctuary, several stones are positioned throughout the building, amplifying their power, and the sanctuaries themselves are being carefully positioned to follow the same resonance pattern, allowing each additional sanctuary to further amplify those nearby. When complete, this will create an enormous magical lattice capable of sustaining the darkness enchantment throughout the Sleeping Lands.
Providing sufficent magical energy to empower this ritual would be quite the undertaking, particularly for the Night Watch as they have few Magi in their ranks. Several ideas have been discussed among senior members of the organization, up to and including desperation tactics like devising a ritual of blood sacrifice to capture the magical abilities of a ritually murdered magus to empowering the ritual. Currently, Onyx Ida, a powerful magus who has managed to keep their association with the Night Watch secret, is in the Iron Hills to investigate if the destruction of the Anchor there offers any means of solving this problem.