Somewhere inside this cube is a twisty, turn-y, 3-dimensional path that will take your marble from Point A to Point B. The start and end corners are marked with little tabs. This maze is almost a labyrinth (a single path with no dead-ends) but not quite, so don't be fooled. Fiendishly difficult, but hey, at least I didn't make the outside surfaces solid!

The cube is 59 x 59 x 59mm and the marble is 12mm dia.

Update: ma-unique has alerted me to his very similar cubic maze design. Check out his excellent Challenger Cube posted back in 2020.

Printing
The cube and marble all print as a single piece without supports. Use a 0.2mm layer height and a 0.5mm line width. The marble (located at the starting tab) is held in place with 4 small tabs. Cut these away with diagonal cutters or a knife after printing. If you have any stringing, clean that up (a heat gun works great) before starting to play. Also, if there are any errant filament strands that didn't quite bond with the bridging, pull those out with needle nose pliers.

UPDATE:
Printing the marble in-place makes it the same color as the cube, and hence, a little more challenging to see what's going on. I've just added files for printing the marble and cube separately so that you can make the marble a different color. Print the marble first, and then when printing the cube, pause the print anywhere between 12 and 14mm in height and drop the ball into the starting position before continuing the print.

Playing
The start position is in the lower front left corner, marked with a little tab. The end position is in the lower back right corner, marked with another tab. Tilt the cube every which-way to cause the marble to roll along the path. If you get fed up and want to cheat, I've included an STL file (inside Maze-Path.zip in “other files” ) with just the path that you can look at to help navigate. Note that the path file does not include several dead-ends, so watch out for those, even if you are cheating!