This may seem like a stupid question, but which is the correct term to use in which situation?

1) Your main character is in a cave and wants to leave. Character goes to the exit/entrance. (I would say exit as that's the action the character is wanting to do)

2) Your outside and want to enter a cave. You go to the exit/entrance. (Entrance, as you're trying to Enter the cave)

But now, if these situations occur at the same time:
3) Main character is in the cave about to exit but someone is at the exit/entrance of the cave.

Do you take it from the perspective of the character you are currently describing or of the perspective of the main character in the scene?