George's Expanding Box

Print three copies of the basic piece, and three copies of its mirror image (I recommend using a different color).  No supports are needed, there is a 2 cm bridge at 2 mm height.  [To mirror a piece in PrusaSlicer, simply select it and then Mirror → Along X axis.]

I include the basic piece in two sizes.  The large (Unit5.0) version makes a 6 cm cube (~10 hours printing), the small (Unit4.0) version makes a 4.8 cm cube (~6 hours printing).  I used 0.2 mm layer height, the movement may be smoother if you reduce this.

Assemble into a hollow cube (box).  This is not easy.  Start with 3 identical pieces, and figure out how they go together.   Then add the remaining three pieces.  Rubber bands may be useful.  Please share any assembly tips in the comments.

After it is assembled grab opposite faces and pull them apart, the box will expand.  Push them together, the box will contract.  Just don't pull too far!  The large box can expand from 6 cm to almost 10 cm.