Cursed Fortress

My beloved Duke — I bring urgent word on wings of haste! Tales emerge to the North of the River Brienne. The townsfolk describe the spectre of an enormous, black fortress. Those who have seen it would have you believe it appeared out of thin air. Certainly there are no prior records of such a citadel.
This forboding structure they speak of... it shifts and shimmers. To fix one's gaze for more than a moment would surely drive a pious man to damnation. There are the other sightings, graver still. Accounts of strange weather; sandstorms, blizzards and mountains of fire, erupting from the earth. Once green pastures of our dear Quenelles, drying to dust. We cannot yet say what horrors might emerge from these blasted wastes.
I have attached a map, though the exact location I cannot be certain. Inexplicable as it sounds, the structure can move! Surely it has done several times since last sighting, but the location marked was my last coordinate measured.
We must ride with haste to this cursed fortress and reclaim the virtue of our land.
May the lady bring us strength...
