Invisible brush/room

How to make bsp brush or static mesh (box) invisible from outside and visible from inside only? Basicly i guess proper material needed for this. Tried invert normals which resulted just to make room content visible from outside, set refraction mat, but basicly it’s not what i want, i guess it’s incorrect methods. Such faking probably can be really usefull for outdoor levels when y want player to jump to some room which is outside of level itself. I’m thinking maybe about some cull distance volume, but it’s just last hope method and not sure it’s gona work.

just slap a masked material onto the outside with 0 opacity