How do you enter the Pirates Cove in Majora's Mask?

ok, its Pirate fortress first off (not to be rude) and once you get the Zora's Mask you swim down to the bottom of the sea, there near the fortress. Down near the bottom is 4 or 5 panels that have skulls and cross bones on them. pick the one second to the right and swim into it. This will open a cave leading into the fortress.