Start by 3D-printing a cube with a stair-step motif subtracted from it:
Eight of those cubes (“octants”) assemble to form a cube with a cavity on the inside:
One octant is missing a corner, which gives access to the cavity:
Put randomly-oriented octants, coated with a release agent (vegetable oil), into your form jig with integrated vibrator (made from a cheap random orbital sander):
Fill the form with concrete, vibrating out bubbles:
Wait for the concrete to set, then remove the octants. Grind the sprue off the cast module:
Make lots of cast modules, changing the orientations of the octants each time. The modules fit together corner-to-corner.* Stack them to make totem sculptures:
* Not entirely true. There are actually two sets of octants that are mirror-images of each other. Right-handed octants fit together with left-handed ones.