The entire mansion seems to stretch on before you, every hallway going on ceaselessly to the very limits of your sight. Every wall seems to be lined with doors, all of them leading to fairly similar little rooms. In fact, none of the doors seem particularly unique. However, as you move deeper and deeper into the mansion, you eventually find yourself standing before a rather particular door.
This door doesn't really look all that special. It's virtually identical to every other door in the building. It doesn't feel any different from the other doors either; it has the same smooth, well-crafted feel of varnished wood that all the others do. It certainly doesn't smell any different from the other doors, and you aren't about to taste it. Suffice it to say that nothing about the door is unique. Even so, you can tell that it IS unique. You know not what pulls you towards this door, only that you are pulled to it. In fact, the door seems downright suspicious because of how it manages to be completely mundane and yet completely unique all at the same time. Still, suspicion alone isn't enough to stop you. This door is something extraordinary, for reasons you couldn't hope to understand, and so you have to open it.
Carefully, you reach out a quivering hand, shaking both with excitement at uncovering the mysteries behind this spectacular door and fear at what might lurk within the room it hides. Slowly, you turn the knob, your anticipation growing with every passing second. Carefully, you creak the door open... and what you see stops you. Behind the door, there is blackness. It shimmers at times with a glimmer of light, reflected from a nearby window or a lamp, but otherwise it is merely black. Even worse than what you can see, you can almost feel the very being of this... whatever it is, and that being is black. There is nothing else here but black, unwavering, unmoving.
Suddenly, it moves. With the crushing force of a tidal wave, the solid black turns to liquid and slams into the hallway as you barely manage to roll out of its path. Turning back, you can see it flooding towards you, pouring like a horizontal waterfall straight at you. You run, but it only follows, flowing around every twist and turn, always covering that behind it. You become aware that it's gaining ground, that it'll be upon you within a moment, that your efforts to escape aren't nearly enough. With no alternative, you dive into a room and slam the door shut behind you, hoping that it'll hold back that terrible shiny blackness that seeks to consume you.