Solved
Door Colliders and Visibility
How can a door with a collider only be visible to players after they enter a room, while also allowing other players to enter through the same entrance? Like in Spy School when players reach the finish line.
Those are planes. The easier way to reproduce this technique is by adding a plane to the world (from the shapes menu), and place in a way that it looks like a wall. Now walk towards it from the side that is visible and you'll notice that it's collidable. Now go around it; first thing you'll notice is that it looks invisible. Also, walking in that direction will not stop you from passing through it. This happens because faces are only collidable from their normal side.
