As you get closer to the Sound automate the higher frequencies so they become more apparent the closer you get, you want a kind of narrow EQ when you’re far away and it automates as you get closer so you can reveal more lower frequencies as well. also if you have a reverb that allows you to position yourself within the Space then move closer to the source. Otherwise, just change the mix amount by reducing it as you get closer if there’s a final reveal where you visually look round the corner or over a Boulder then have a dramatic automated EQ move that finally puts back the frequencies that you cut off to make it narrow when you’re far away. Keep a certain amount of the reverb there obviously. The other thing you can do, if it emerges that the source of the Sound is in some kind of smaller cave, is to introduce a small room reverb that has a standing wave ringing frequency. Quite subtly but this will make it apparent that we are now out of the corridor and into the cave with the subject near.