Box of Secrets (3.5e Equipment)
From D&D Wiki
Box of Secrets: A Box of Secrets, is similar to a Portable Hole, in such ways that it can carry lots of items in it. You simply open the boxes lid, and then you can place objects in them. These boxes are extreme magic, in such ways as it has an unlimited carry capacity, meaning that you can put as much as you want into it and nothing will happen, except that you now have a bunch of items in a miniature box. On rare occasions, (10%), every time you open the box, a creature will come out if it. There is a 40% chance that it will be friendly, and a 60% chance that it will be hostile. These boxes are very powerful, that If you were to place any object that is extra dimensional into it (Portable hole, bag of holding, folding boat, well of many worlds), it would create a hole in time and the possessor would be trapped there forever. There are only 6 of these boxes however, all currently reported to have known locations. Those locations are: 2 are in Ravenloft, 2 are on the prime material plane(earth), and the other 2 are in the Acheron plane. One of the boxes in the Acheron plane currently has a master. That person is Thanara from Yomesh.
CL ; ; Cost 6,000xp; Market Price: 20,000 gp