I have a part that has CanCollide and CastShadow disabled. And, has Anchored enabled. If I am outside the part it is visible if I get the camera inside the Part it is not visible. ¿How do you make a part visible from the inside?
Try making it a union. Duplicate the part, shrink it ever so slightly on all sides, and then negate that inner part. Union that with the outer one. Then you should have a hollowed out box that you can see from the inside as well as the outside.
(sorry if my english is bad) you can also put "walls" around the part (cover it with other thin parts) i did it with a water block i made