I've started my first modeling project and it requires some sort of invisible wall. This invisible wall needs to allow NPC's to react to the player. In addition it needs to block physical and magical projectiles, summons and weapon collision. The method needs to leave the Player or NPC's untouched by scripts or records. I'm guessing some sort of Collision?.

Although not required for the project it certainly would be preferable if I could make it like a one-way invisible wall. A wall that prevents the player entry but allows player projectiles and weapon collision. Basically the player can kill anything behind the wall but the NPC's cannot.