Forbidden Passkey (Patreon)

Wondrous item, rare (requires attunement)

A blood-stained key of uncertain origin. As a bonus action you can have this key appear into your hand even if you are not on the same plane of existence.

The Blue Room. If this key is inserted into any keyhole, you can open the door to an extradimensional stone dungeon constantly pooling with blue blood. The room is a 15-foot cube with no other windows or doors and can only be entered or exited through a door created by this property. When the door is closed the room is pitch black and creatures inside it can breathe. If a creature uses this key on the door of the Forbidden Room from the inside, it opens to the last doorway it was connected to.

Siphon Knowledge. If the body of a dead humanoid is inside the Forbidden Room, it does not decay as the room keeps it from rotting. After you finish a long rest, you can choose to gain proficiency in a skill or a language of your choice that a dead creature within the room had in life. This benefit lasts until you finish a long rest.

Too long did Bluebeard's terrible spree of murders continue, a crime discovered far too late for justice to be brought upon the monster responsible. Attempts to erase the tale and bury all traces of it were made, but one detail was amiss: the key. No matter how long and hard the search, the item of singular significance could never be found. Perhaps it was lost to time, or perhaps the terror of the bloody room persists to this day.