Meshing Complex Hollow Geometry

Dear Users,

I have a cube-like geometry that has multiple holes in it, where the holes don't go through the cube straight, but rather follow a spline curve. I would like to mesh the geometry but, after many hours of partitioning, can't seem to get it right. Whenever I try any bottom-up method, some of the holes are meshed through. I would very much appreciate any sort of tips that I can get for my mesh. Thank you!