The Celestial Prison is an immense sacred containment complex hidden beneath the northern mountains of the Winterlands. Commonly called the World's Largest Dungeon, it was constructed in the mythic past by the celestial powers associated with Cael-Seryn.

The prison was created to contain beings and forces that could not safely be destroyed, banished, or allowed to remain within the wider world. Its full dimensions remain unknown. Surviving evidence suggests that it may be less a single dungeon than a network of chambers, wards, locks, and metaphysical seals extending beneath a considerable portion of the region.

Much of the prison remains unexplored. Even the scholars and religious authorities who know of its existence possess only incomplete records concerning its builders, original purpose, internal structure, and prisoners.

The celestial inhabitants of ancient Cael-Seryn were among the principal architects of the prison. Their work combined divine warding, celestial law, arcane seals, and living anchors placed throughout the northern mountains.

Cael-Seryn served not only as a holy city and observatory, but also as a center of knowledge and responsibility connected to the prison. Many of the city's oldest rites, archives, and institutions appear to have supported the maintenance or observation of the prison's seals.

The exact date of construction and the identities of any other participating powers remain unknown.

The prison is divided into multiple wards, though their total number, arrangement, and individual purposes have not been established.

Known references include the Seventh Ward, whose surviving records were catalogued within the Celestial Roster of the Seventh Ward. This roster allowed the Aegis Order to identify and contact the Celestial Dragon Seraphel Aundren.

The prison's defenses appear to include:

• Physical barriers and sealed chambers.
• Divine and arcane locks.
• Metaphysical seals anchored to locations outside the prison.
• Celestial custodians or observers.
• Living ward-anchors such as Belatu-Cadros.
• Ritual systems that may respond to particular bloodlines, blessings, or supernatural marks.

The exact relationship between these systems remains under investigation.

Belatu-Cadros is a great Celestial Tree believed to anchor several of the prison's metaphysical seals. Its corruption has caused it to produce a dangerous black sap associated with Far Realm portals, aberrant transformations, and the corruption of powerful magical devices.

If Belatu-Cadros is destroyed or completely overtaken, at least one of the prison's remaining barriers may collapse. Purifying the tree may therefore be essential to stabilizing the prison.

In the modern era, agents of the Empire deliberately weakened portions of the prison's ancient ward network. The resulting disaster became known as the Breach.

Daemons, undead, aberrations, and other unnatural creatures escaped into the surrounding Winterlands. The nearby settlement of Westgate was overrun, forcing its surviving inhabitants to flee or fortify themselves until relief arrived.

Forces from Wintershield and Valkenbane Academy eventually reinforced the regional barriers. These efforts prevented the complete collapse of the prison, but they did not repair the underlying damage.

The prison still holds. Its locks, however, continue to fail.

Far Realm influence has spread through portions of the prison's foundations and ward network. This corruption does not merely weaken the structure—it alters the prisoners, seals, and surrounding environment.

Two major corruption fronts are currently known:

The corruption has become dangerous enough to frighten even some of the fiends imprisoned within the complex.

Diantha is a fallen Erinyes imprisoned in one of the deeper portions of the complex. She cannot yet leave her prison physically, but the failing wards allow her to reach the outside world through dreams, visions, reflections, and whispered promises.

Diantha has manipulated mortal agents into damaging systems connected to the prison. She seeks escape partly out of ambition and partly from fear that continued exposure to Far Realm corruption will transform her into something no longer infernal—or comprehensible.

The names and natures of the prison's other inhabitants remain largely unknown.

Seraphel Aundren is a Celestial Dragon identified through the Celestial Roster of the Seventh Ward. The Aegis Order contacted Seraphel through the dream-city of Cael-Seryn.

Seraphel confirmed that the prison remains sealed, but warned that its locks are failing. He has provided the Order with limited information and has promised future aid in understanding or restoring the damaged ward network.

Whether Seraphel is physically imprisoned, serving as a custodian, or bound to the prison in some other fashion has not yet been fully established.

The mysterious Dragonmarks carried by members and allies of the Aegis Order may be connected to the Celestial Prison.

The marks frequently appear following acts of purification and seem to protect their bearers against certain forms of corruption. Current theories suggest that they may function as:

• Keys to ancient ward systems.
• Protections created for celestial custodians.
• Signs identifying individuals capable of entering corrupted areas.
• Living replacements for damaged portions of the prison's defenses.
• Warnings that the marked have become part of the prison's fate.

None of these theories has been conclusively proven.