Backpack of Holding

Appearing as a normal sized backpack, this item, when opened, shows an extra-dimensional space equal to a 40' high by 40' wide by 40' deep.  Placing another extra-dimensional bag or receptacle into this will cause the items to explode, causing a rift between the Prime Material and Astral Planes, sucking those who are within 60' of this rift into the Astral Plane.  The explosion will destroy both receptacles and the contents will be scattered into the Astral Plane.