Bag of Holding

A container with more space within than is right or natural

Recipe
Prepare a bladder, unmarred, of the blink dog, in a pultice of finely ground hitren, then boil the bladder for 3 nights and 3 days in a mixture of bile from a night shifter, reciting the chant of Wastri... on the 4th dawn rinse the mixture off in a basin of astral effluvient... let dry and then dress with plain leather as an aperture..."