With the defenses gone, cross the metal slab onto the next platform - though the platform beyond has no bridge. Use the metal block as cover - at which point you can take it out either with your weapon, or by using the Magnesis Rune to send the block crashing into the Mini Guardian, or even shove it off into the water below causing it to explode. While not as imposing as the larger Guardians, this Mini Guardian can still deal major damage with its timed laser blast. On the other side of this path lurks a Mini Guardian. Wrangle it with the rune to push aside the blocks creating a new path. Here you'll find a large stone wall blocking your path, but checking your Magnesis Rune you'll find one of the blocks is in fact metal. Follow the path along the water to climb stairs to the other room. Using the Rune, target the metal plates in the middle of the room to lift them off the floor to reveal a path below the gate. With this rune, you'll be able to manipulate metallic objects found both in the shrine and in the world at large.
To the left of the gate is a pedestal you can place your Sheikah Slate on to gain access to the Magnesis Rune. Entering the Oman Au Shrine you'll see a large locked gate before you, and several metal tiles on the floor.
