My players figured out quite fast that it was a dragon's nest, because they had Elor's map with the "nest" comment, and being so large a cave just said "this must belong to a dragon!"
Anyway, remember it hasn't been used in a while, so no loot here I guess.
We are one adventure away from completing the campaign (though I left most of the Orb of Unlife plot out because of time restrictions, two years playing three times a month seemed like enough for me).
The shards were not a problem in the end. The party knew that the Dir platform was going to be dangerous, so they spent some time buffing themselves. Then they jumped using the small columns, and as soon as they reached the platform saw all of their efforts turning off, they screamed "go back go back!" and regrouped some columns behind. Then, in a surprisingly knowing way, decided to "test the size of the anti magic field" by going up and shooting crossbow bolts with light spells on them, and with this they understood the height, used some flying and levitation spells, and landed right near the tree. They even said "I wanna do some locate hidden under this pool" and found the helm!
Next week after we do the closing scenes and final battle I'll come back and tell you how it went.