That is the Ice Chest. If you go to Glitter Gulch Mine, and go towards the waterfall where, to your right, you can access the deeper mines, and below there is a large pool, dive into the pool. You should see a rock with Kazooie's face. Use Kazooie's Torpedo move to break it, and swim through the resulting tunnel.
If you have collected the Ice Key in Jinjo Village, then you can continiue. If not, go back!
Once inside, you will be met with a large, icey treasure cheast. Use the Ice Key to open it, and you should be rewarded with a huge Globow!
Now, head to the Plateau area of Isel o' Hags. Go inside Humba's Wigwam, and thwo the Glowbow into the pool. Jump in to get the prize.
It has been mentioned countless times before, and if you had just looked around a bit, you wouldv'e found out that it was a regularly occuring feature.
But, after 8 years, don't you think that we would have found this already?
EDIT: OH GOD DAMNIT BOTTLES.