Arcane Sanctum

You infuse the Weave itself with your arcane essence, calling forth a Sanctum — a permanent dwelling that resonates with your personal magic. It manifests as a graceful home touched by your essence — perhaps a smooth stone retreat veined with gentle light, a quiet crystal pavilion, or a stately tower whose walls shimmer when you pass.

The Sanctum’s interior is roughly the size of a large urban home and includes:

• Bedrooms, a lounge, study or library, kitchen, washroom, and storage chambers.

• A central Focus Chamber, the heart of the dwelling, whose design reflects your magical nature — a crystal obelisk, a mirror pool, a sigil-etched dais, or something entirely your own.

• Magically sustained comforts such as warmth, clean water, and soft light, though mundane upkeep like cleaning still require labor.

The Sanctum cannot create food, wealth, or living beings.

Optional Rule — Bastion Integration (D&D 2024).
If your group uses the Bastion rules, the Sanctum qualifies as your Bastion if you have none. Its magical foundation replaces the need to construct the building manually, but you must still possess or secure the land on which it stands.

• You can perform Bastion Operations from within the Sanctum as normal.

• The Focus Chamber may function as one Bastion Facility of your choice (Library, Laboratory, or Study) for the purpose of Bastion features and upgrades.

• If the Sanctum is destroyed, suppressed, or dismissed, your Bastion becomes inactive until the spell is recast.

• When you recast Arcane Sanctum in the same or a new location, it automatically restores your Bastion and any Facilities it contained.

Arcane Resonance.
The Sanctum’s magic aligns with your soul, subtly shaping the flow of arcane energy within its walls.

• Allies you designate within the Sanctum have advantage on saving throws against being charmed or frightened.

• Unaffiliated spellcasters experience interference in their magic. While within the Sanctum, they have disadvantage on concentration checks and when they cast a spell they must succeed on an Intelligence saving throw (DC = 8 + your proficiency bonus + your spellcasting ability modifier) or the spell fizzles harmlessly.

• A creature that succeeds on this saving throw three times becomes attuned to the Sanctum’s energy and is immune to the interference for 24 hours.

Security and Detection

The Arcane Sanctum is more than stone and mortar — it is a magical fortress.

• The outer structure blends with its surroundings, shielded by an illusion and warding field.

• To detect or even perceive it as unusual, a creature must succeed on a Perception check (DC = 10 + your spellcasting ability modifier + your proficiency bonus).

• If a creature investigates with magic (such as detect magic or true seeing), it learns that the area hums with protective abjurations but cannot automatically bypass them.

• The Sanctum has AC 17 and 100 hit points. If destroyed, it collapses into inert mundane material, which may be restored if the Sanctum is recast in the same spot.

Dispelling the Sanctum suppresses its magical effects (wards, interference, etc.) for 24 hours, but the structure and guardians remain intact.

Guardians

When you cast Arcane Sanctum, you may expend additional spell slots to summon guardians from summoning spells you know and have prepared (such as Summon Aberration, Summon Construct, Summon Fey, etc.).

• Guardians remain permanent for as long as the Sanctum exists but cannot leave its boundaries.

• Recasting Arcane Sanctum replaces or resummons all guardians.

• Guardians automatically regain all hit points after 8 hours of inactivity.

• Guardians do not grant experience points when destroyed.

• Maximum CR or combined spell level: equal to the highest additional spell slot used × 2 (minimum 1).

• Guardians must come from legitimate summoning spells you can cast.

Higher-Level Casting (Slot Upgrades)

• 6th-Level Slot: The Sanctum becomes dimensionally anchored — teleportation and planar travel into or out of it fail unless permitted by you.

• 7th-Level Slot: The Sanctum expands to include a specialized arcane facility — a library, alchemy chamber, or workshop suited to your magical discipline. When using the Sanctum as your Bastion, this facility counts as two Bastion rooms for purposes of research or crafting downtime activities.
  Additionally, research or crafting related to your spellcasting tradition (such as scrolls, potions, or magical items) is completed in half the usual time while performed within the Sanctum.

• 8th-Level Slot: A Teleportation Chamber manifests — a crystalline hall or runic nexus containing a permanent Teleportation Circle keyed to your unique arcane sigil. You and your attuned allies may use it to cast Teleportation Circle from within the Sanctum without expending a spell slot or material component, once per dawn.
  In addition, you may attune the Sanctum’s circle to one existing permanent teleportation circle whose sigil sequence you know, creating a stable two-way link between them. Either end of the link can be changed whenever you recast Arcane Sanctum.

• 9th-Level Slot: The Sanctum becomes a true arcane bastion. Guardians gain resistance to nonmagical damage, and the Sanctum’s wards extend to a 60-foot perimeter, suppressing divination spells and scrying.

Integration with Bastion Growth (Optional Rule).
If your Sanctum serves as your Bastion, its size and facilities expand naturally as your character level increases, following the Bastion rules in the Dungeon Master’s Guide (2024).
Upcasting Arcane Sanctum does not alter this baseline growth, but higher spell slots empower its magical properties — expanding its protection, improving its guardians, or enabling planar anchoring and teleportation features as described above.
If the Sanctum is ever dismissed, dispelled, or destroyed, your Bastion remains dormant and inaccessible until you recast the spell. When restored, the Bastion returns at its full progression level.

Casting Limitations and Recasting

• You may only have one Arcane Sanctum at a time.

• Casting the spell again relocates the Sanctum and its contents to the new site, replacing the old one.

• Items and creatures inside remain safe if the spell or structure is destroyed , dispelled or suppressed.

  If the structure is destroyed, the caster is harmlessly deposited near its remains. All other creatures and objects within are drawn into the spell’s essence, preserved in a dormant state until the sanctum is recast.

  If the caster dies before the sanctum is restored, the binding weakens. After 7 days, any stored creatures are released safely at the site where the sanctum last stood, while unattended objects appear nearby. If no safe space exists, the magic delays release until one becomes available.

• When recast, all guardians are automatically restored or replaced.