I wrote a solver for a similar puzzle: IIRC it was 3x3x3 with different shaped pieces that left some space unfilled. Some of the pieces had holes and you additionally had three 3-long metal rods to place inside somewhere. I ran my code and it didn’t find a solution. Best it could do was fit all wooden pieces and two of those rods through holes inside the pieces. [Spoiler] Turns out, the solution was to ignore to rods first, leave a 3x1x1 “tunnel” and put all three rods in there, completely ignoring the holes in the wooden pieces. I remember being slightly annoyed :-)