module menger_schwamm_neg(iter, x, y, z, w) {
    union() {
        translate([x,y,z]){
            cube([w/3, w/3, w*1.1], center=true);
            cube([w/3, w*1.1, w/3], center=true);
            cube([w*1.1, w/3, w/3], center=true);
        }
        if (iter > 1) {
            for (xo = [-w/3:w/3:w/3]) {
                for (yo = [-w/3:w/3:w/3]) {
                    for (zo = [-w/3:w/3:w/3]) {
                        menger_schwamm_neg(iter-1, x+xo, y+yo, z+zo, w/3);
                    }
                }
            }
        }
    }
}

module menger_schwamm(iter, x, y, z, w) {
    difference() {
        translate([x, y, z]) cube(w, center=true);
        menger_schwamm_neg(iter, x, y, z, w);
    }
}

menger_schwamm(1, 0, 0, 0, 3);