you put a water bomb on this place where bubbles are kinda coming up in front of the wall where up above the rocks are blocking the entrance. once that bomb goes off, the vent should be strong enough so that when you put another bomb in the same place, it will carry it up to blow up the rocks. and, you don't have to buy the hylian shield, but you definitely should because it will never burn. remember, a good deed deserves a rep!