Shade (animal)
Shades are a type of spirit characterized by an inky-black appearance and complete inability to produce sound, in effect rendering it virtually impossible to discern their mortal origin. Beyond their appearance and extreme aversion to daylight, perhaps most notable is their ability to raise new shades from slain foes, and there have been several historical incidents of cities getting completely overrun and destroyed by a shade infestation.
Shades are, mercifully, rather hard to encounter in most of the world unless one goes out of their way to search of the kind of unnaturally dark places that they normally inhabit. Great pains are made by most societies to root them out whenever they emerge near civilization, as an infestation can easily spiral out of control in the span of a single night and leave an entire settlement decimated.
We have ample reason to believe that the ruin in front of us is host to a group of shades. The darkness lying beyond the entrance is so pitch black that one feels it might just devour any who enter.