Griffin School Armor (The Witcher 3: Wild Hunt)

Under water))

There is a cave under the water, which I never found, but by stupidly clicking the B (jump) button, I could jump onto the wall to the right of the raised bridge (however, it is difficult to do this, Geralt rolls down and is generally not provided for by the developers), somewhere with the fourth attempt succeeded.

there is a cave near the power stone between the island and the mountain