Go to where you found Deep Blue and look around, there should be an entrance that is blocked by boulders, use Thermites bombs to clear the way.
Once inside go left and use Major Ruins rush to go up the ramp, there will be a water spirit there but you can easily kill him by using Deep Blue and Pummel Weed.
Then use any Elemental to destroy the Treasure chests and you should get a total of 200 runes.