  It is a $300$ year old counterintuitive observation of Prince Rupert of Rhine
that in cube a straight tunnel can be cut, through which a second congruent
cube can be passed. Hundred years later P. Nieuwland generalized Rupert's
problem and asked for the largest aspect ratio so that a larger homothetic copy
of the same body can be passed. We show that cubes and in fact all rectangular
boxes have Rupert's passages in every direction, which is not parallel to the
faces. In case of the cube it was assumed without proof that the solution of
the Nieuwland's problem is a tunnel perpendicular to the largest square
contained by the cube. We prove that this unwarranted assumption is correct not
only for the cube, but also for all other rectangular boxes.

Metric Geometry