Luminol was the capital city of the elven kingdom in the Eladain wood. It’s silencing was one of the dark events that led to the forest becoming known as the Forest of Woe.
Luminol seems to be near the heart of the swampy corruption that has taken root in the forest. Since journeying into the city, the heroes have discovered an apparent collaboration between Medusae and demons to turn the elves into statues ripe for demonic possession. The Starshield prevents outside aid from reaching Luminol … but perhaps more importantly, it keeps the dark forces inside it from roaming free.