The Shadow Fortress

Imagine a dark, bewitched fortress that appears sporadically and terrorizes a fantasy kingdom.

This writing prompt centers around the sudden and unexplained appearances of a frightening fortress that casts a significant shadow over a kingdom, inducing dread and panic amongst the residents. How does this intermittent threat manifest itself? Explore the terror, the speculations, the myths, and the brave or foolhardy attempts to venture into the fortress, and the aftermath.