Demiplane

Prerequisite: Level 17, base cost 15,000 gp.
Facility Rating: None
Supply: None
Action: Empower (character with Arcana proficiency)

A door up to 5 feet wide and 10 feet tall appears on a flat, solid surface in one of the other facilities aboard your vessel. You choose the location. If you are aboard your vessel during a Vessel Facility Turn, you can relocate this door to another facility aboard your vessel.
Only you, your party members, and your crew can open the door, which leads to a Demiplane that takes the form of a stone room. The Demiplane exists in an extradimensional space and therefore isn’t attached physically to other locations aboard your vessel. Neither the Demiplane nor its door can be dispelled.
You can store up to four units of cargo within the demiplane, assuming they can fit through the door. Attempting to take a Bag of Holding, Heward’s Handy Haversack, Portable Hole, Compressed Cargo (see Cargo rules) or similar item inside the demiplane instantly destroys both items and opens a gate to the Far Realm (see the sidebar on Extradimensional Spaces in Magical Items).
The gate originates where the door to the demiplane is aboard the vessel. Any creature within a 10-foot-radius Sphere centered on the gate, and everything (including creatures) within the demiplane is sucked through it to a random location in the Far Realm. The vessel receives 88 (16d10) Force Damage, the gate then closes, and the facility is removed from the Vessel. The gate is one-way and can’t be reopened or prevented from closing..

Empower Options

When you use the Empower Action with this facility, choose one of the following options:
Empower: Arcane Resilience. Magical runes appear on the Demiplane’s walls and last for 7 days. Until the runes disappear, any character gains Temporary Hit Points equal to five times their level after spending an entire Long Rest in the Demiplane.
Empower: Fabrication. While in the Demiplane, you can take a Magic action to create a nonmagical object of your choice from nothing, causing it to appear in an unoccupied space in the Demiplane. The object can be no bigger than 5 feet in any dimension; can’t have a value over 5 GP; and must be made of wood, stone, clay, porcelain, glass, paper, nonprecious crystal, or nonprecious metal. You must finish a Long Rest before you can take this action again.