GOT IT! Need to open the door at the ROCK WALL in the jungle area, which is where the mirrors go. I was at the SHADY WALL near the INTERSECTION on the western part of the main game area. Thanks all for steering me to a new location!

Am at the shady wall, have opened the door, have the jar and can blow mirrors and aim them. For the life of me I cannot find a combination of mirror locations and directions that will send light into the dark underground rooms. Can someone tell me exactly which room the first mirror goes in, and how...