A 2-meter cube at the world origin with a round hole punched straight through it: a cylinder of 1 meter diameter, centered, running clean through the top and bottom faces. Apply the boolean so the result is a single mesh with an open channel — the camera can see straight through the cube.

The floor is the hole. The ceiling is the finish: a small even bevel on both rims of the channel, shading with no boolean artifacts, and one simple, pleasant material.