"Tap... tap... tap... tap..."
Clear, steady footsteps with a distinctive rhythm abruptly shattered the almost eternal, soul-tightening silence of this domain.
The sound echoed through a broad corridor of ancient black basalt whose end lay beyond sight. Its walls were smooth as mirrors, yet strangely absorbed light rather than reflecting it, making the echoes seem particularly hollow and cold, as though they came not from physical vibrations but from blows struck directly against the mind.
This was the deepest part of the Imperial Palace, a domain beyond the knowledge and authority of ordinary people and even most Space Marines: the Dark Cells.
This was no prison for ordinary captives, but the final tomb where terrifying secrets and forbidden beings were buried, sealed, and suppressed—things so dangerous, so blasphemous, so ancient that even erasing them entirely from humanity's memory would not be "safe" enough.
Its depth and complexity far exceeded the magnificent structures on the palace's surface, like the dark, twisted roots of a vast Tree sunk deep into the earth.
As the footsteps drew closer, pairs of glowing eyes silently lit up in the alcoves on either side of the corridor, which had previously blended almost completely into the darkness.
Then the scrape of metal, the faint hum of energy fields activating, and the barely audible hiss of armor-joint hydraulics coming online broke the stillness.
The Shadowkeepers of the Dark Cells.
They were the elite of the Adeptus Custodes. Their armor was heavier than that of ordinary Custodians, coated in a darkness that absorbed all light.
They were the wardens of this living tomb, living headstones personally appointed by the Emperor, sworn to maintain their vigil until the end of time.
Any unauthorized being who set foot here, regardless of identity, would meet only the most immediate and merciless destruction.