Below the Frozen Waves

Steps

 * 1) Travel down to the Ry'Gorr caves, called Demon's Delve.  South side of main island, deep under water, cave entrance at 59,-99,391.  Quest updates a few steps after you hit land.
 * 2) Examine the suspicious cave-in to the north, follow right wall to -11,-67,157
 * 3) Return to Thirin Veliumdelver.

Rewards

 * At least 2s 40c
 * One of the Following:
 * Choker of Elemental Might
 * Earring of Frozen Earth
 * Band of Marr
 * Deceitful Choker