I found by accident but it works every time. Not sure the implications but a spot by island if you jump off rock in the water instead of hitting water it sends into parachute mode and you free fall under water as under the map! Its wild and deploy parachute and glide under the lake but no water visible just the deep bottoms of map. Eventually it unharnessed me and I began walking everywhere but couldn't find a way back up but could have walked forever. I tried again and it worked no problem again.