Shining Citadel

The Shining Citadel is a fabled fortress on the Plane of Shadow. A legend tells that the plane was once a normal demiplane but when an order who venerated the plane's creator built the Shining Citadel, they used the plane's light, colour and life to power it, and the Plane of Shadow was stripped of these things as a result. No being on the Material Plane is thought to have found the citadel, if it exists.