Not sure if this has been done yet but how a bout a box existing in the second dimension only. I think it would be a good thing to write about.
So it's like a portable hole or ACME hole kinda hammerspace thing?
I dunno. I feel like the concept has already been portrayed in numerous ways by popular media.
Of sorts but everything stored in it is stored in 2D so there are limitations and the laws of physics will be different. I thought it would be a cool idea the most I have seen is a 2D portal to a 3D storage space.