I made this cube inside of a cube, where the smaller cube is too big to be removed from the holes.

I used a wood called Bubinga which is about 2x harder than oak, and smells like chocolate bananas when you cut into it.

I got a block of wood from lee valley, this was about $30.

You get the effect by using a forstner bit to bore a hole into each face the same depth on each side until just the corners attach to it. Thinking in geometric shapes, six intersecting columns would create a space for a cube inside, which is how this is done. The trick is to stop drilling before you go too deep, and use a sharp knife to pick out the edges.

Then you can carve or sand out the inside of the wood to complete the look, and give it a nice finish.

With a large enough block of wood, you can nest these cubes as far as the tools will permit you to.