... I overlooked that. -_-"
I did beat Eyelord unharmed, though. So thanks!
I got the Lv4 Master Sword, and silver arrows.
So how to enter Turtle Rock? I got there, at least... and that heart piece in the Light World near that. (17 hearts + 2 pieces.)
Turtle Rock requires you to return to Death Mountain, and go to the Tower of Hera. Then go eastward until you see an area with three stakes in a triangular formation. You'll need to hit them in this order: Right, Up, Left. After this, a portal to the Dark World will show up, which takes you to Turtle Rock. You'll need the Quake Medallion to open the entrance to the dungeon before going in.