The Door of Night by John Howe
Its pillars are of the mightiest basalt and its lintel likewise, but great dragons of black stone are carved thereon, and shadowy smoke pours slowly from their jaws. Gates it has unbreakable, and none know how they were made or set, for the Eldar were not suffered to be in that dread building, and it is the last secret of the Gods; and not the onset of the world will force that door, which opens to a mystic word alone.