This simple looking briefcase is made of tanned brown leather featuring a small handle and two metal clasps keeping it closed. 

A creature who succeeds on a DC 18 Wisdom (Perception) check notices a small switch positioned underneath the handle of the briefcase. A creature who has been made aware of the switch's existence automatically passes the Perception check. 

This briefcase has no distinct features and looks exceptionally bland. The inside of this briefcase has enough space to store the everyday needs of your average traveler or well organized wizard however, when the briefcase is shut and the switch is flipped to the opposite position, something quite spectacular occurs. When this magical briefcase is opened with the switch in the opposite position, any creature will find a ladder leading down into large square space measuring approximately 1600 square feet with 12 foot high walls and a ceiling. The only opening to and from this space is located in a single corner through the briefcase.

The space itself counts as its own pocket dimension. Any items, objects, or even creatures put into this pocket dimension will remain there so. A creature who is left inside of the pocket dimension will not suffocate as the air inside is supplied magically through the briefcase. Any creature who is inside the pocket dimension space when the briefcase is shut is unable to leave the space without brute forcing there way out. A successful DC 16 Strength (Athletics) check by a creature inside the pocket dimension space will be able to burst out of the briefcase and will forcibly open the briefcase wherever it may be. The switch will automatically change to the appropriate position.

If this briefcase were to be destroyed by any means, all contents, objects, and creatures no matter their nature will be scattered to the cosmic winds of the Astral Plane to a random location. Storing other items inside this space that also create extradimensional spaces such as a Bag of Holding, Handy Haversack, or Portable Hole do not cause any magical instabilities.