Originally Posted by Tai_MT
There were two relics I picked up that REQUIRED me to use the Hang Glider to obtain. There's one on an island that I couldn't do the "hack jump" that I'd been using for all the rest of the islands. There was just nowhere to jump up to because of the sheer cliffs on the place. It stuck up about twenty feet high with no slope on it.
Then, there was the one in the ravine. There's a little shrine in the cliffside. I fell to my death ten or twelve times without ever ONCE seeing a way into this little nook. I saw no vines. I saw no alternate paths. I couldn't drop into it... I just went up the hill, grabbed the glider, then flew into the small nook for that Relic.
You and BiggD could very well be right. I only got relics off a couple islands and I was either able to find a place to "hack jump" or there were vines. I stopped getting relics after I got the achievement and leveled up all the way so you are probably right.