Need Help Master Key Shadow Temple (Possible Spoilers)

[NSYNCSUX33]

I am in the Shadow Temple, I believe it is the 8th dungeon. I have made it to the boss door and I cannot find the Boss Key. I'm assuming I missed something rather easy, but I just cant think of what to do. If you could help I would be thrilled. Thanks.

 

[Thorgouge]

you know that room with the bottomless pit that has a giant ledge with the door that leads to the tall room that leads you to the boss room? Theres a waterfall. spin attack with your light blade and jump across then hookshot to the top theres the key.