This fine brown cloth, soft as silk, is rolled up inside a scroll case.

It unfolds into a rectangular strip 6.5 feet in height, and 3 feet wide.

You can take a Magic action to unfold a Portable Librarium and place it on or against a solid wall, whereupon the Portable Librarium creates a doorway.

The door opens to a room that exists on a different plane of existence. Any creature inside an open Portable Librarium can exit the room by opening the door and walking out of it.

From outside the room, you can take a Magic action to close a Portable Librarium by taking hold of the edges of the cloth and folding it up. Folding the cloth closes the door, and any creatures or objects within remain in the extradimensional space. No matter what’s in it, the Librarium  weighs next to nothing.

A closed Portable Librarium  holds enough air for 24 hours of breathing, divided by the number of breathing creatures inside.

Placing a Portable Librarium  inside an extradimensional space created by a Bag of Holding, Heward’s Handy Haversack, or similar item instantly destroys both items and can have a number of very detrimental effects. 

Beyond the door is a cozy reading room and library approximately forty feet across. The atmosphere is clean, fresh, and warm. A fire burns merrily in a hearth, a large glass window shows a tranquil scene, looking down on a snow covered woodland.  Several comfy leather arm chairs are scattered around the room, as are small end tables and magically lit reading lamps. A deep shag carpet covers the floor and the walls are entirely lined with shelves of books. 

Over in a corner, a small stand contains sweet and savory snacks, cookies, fruit, scones, crumpets, cigars, and other treats. A tea kettle heats in the fire, and a wine rack contains a few bottles of wine, port and sherry of various strange and unknown vintages.

A large wooden chest sits against one wall, 3 feet by 1.5 by 2. the chest has no lock, but is bound with heavy brass clasps. A small brass plaque attached to the chest reads

Items left here will not be disturbed by the cleaning staff

Furnishings and other objects within the Librarium dissipate into smoke if removed from the room.

A small brass plaque attached to the wall next to the fireplace says "

Take your ease, weary scholar, but do not linger long when the door is shut."