Complex sentence: Scenes of the main cave entrance are normally filmed in a manner that shows the entrance at an angle because the cave is actually a very short tunnel through the hill, with the rear opening easily visible in a direct shot.
Split into simpler sentences: Scenes of the main cave entrance are normally filmed in a manner that shows the entrance at an angle. This is because the cave is actually a very short tunnel through the hill, with the rear opening easily visible in a direct shot.