Difficult, but worth it!
Do the swordless link trick then ride to lake hylia. Make epona face where the alternate entrance to zora's domain was as a kid. Pull out your ocarina then press "B". Equip your iron boots and walk forword then turn and face the alternate entrance. It will be black. Walk up to it and press "A". You will begin to mount epona, so quickly pull out your normal boots. You'll now be swimming under the ground! Now swim into the alternate entrance from behind. Once there equip your iron boots. You'll see that this alcove actually leads nowhere.
