Get the parasol ability then use the door ahead. Watch for spikes as you go through the water and use the next door to go back outside. Navigate the water by some moving fish along with a Gordo then enter the cave again. Hit the bomb blocks to remove the walls and use the door at the top end to go back outside. You’ll next battle a swarm of small knight in possession of axes and spiked maces. Defeat them all and go through the next door. After a potion by 2 fish, you’ll find the goal.