A reliable check whether an xyz point  is 'inside' or 'outside' a mesh is very costly. Mesh objects are not by definition 'watertight', so the simple 'cast any ray and count intersections' method does not work. On top of that, formally there is no 'inside' or 'outside' unless the mesh is 'watertight', while a labyrinth would effectively have the same effect as watertightness when it comes to casting shadows.