As you descend to the ground here, Groose (remember, the jerk from the Knight Academy?) will decide to hitchhike onto you, making your landing more than a little rough. After conversing a bit, he’ll run to the temple.
After you regain control, use the nearby Bird Statue and speak with Gorko a few times to learn about the Goddess Walls and Gossip Stones – it seems that, if you play the Goddess Harp amongst certain groups of blue butterflies (Blessed Butterflies), you’ll find some special things.
Anyhow, go west and ascend the vinery. Afterwards, go to the Sealed Temple nearby.
Once you’re inside, you’ll watch a scene between the old woman from long ago and Groose. After Link walks forward, you’ll be given a tutorial on how to play the Goddess Harp.
Play it in time with the old woman’s braid – you’ll know you’re doing it right if more lights pop up; trust me, I prefer going by that than the actual music. :P
After the tutorial, you’ll have learned a song, the Ballad of the Goddess. By having played the Ballad, a large stone monolith, the Gate of Time, will appear in the temple. You’ll converse some more, after which the area shakes and the old woman will tell you to go to the bottom of the pit outside.
Outside, go forward and jump off of the ledge, using the Sailcloth to soften your landing. Repeat this until you reach the bottom of the pit. Afterwards, the stone sealing away a very familiar beast shatters, unleashing the dreadful Imprisoned!
Boss: The Imprisoned
At the start of the battle, the boss’s main goal is to walk to the top of the pit and to the temple. This boss will stand upright – how is that important? Well, this boss has four toes per foot (one is in the back). Begin by slicing at the toes on one foot - three hits destroys a toe.
After removing the toes from one foot, the boss will move more slowly, but also summon shockwaves upon stepping down. Avoid these while you proceed to cut off the remaining foot’s toes.
Afterwards, the boss will fall over backwards. Once it does, run around and down the slope to the boss’s head and you’ll notice the stone pillar from earlier sticking out from its head. (I’d go crazy too if I had something like that in my head.) Anyhow, you’ll need to hit it with down-up vertical slices to damage the boss by driving the stone into the head.
After three such hits, the boss will stand back up, charge up the incline at a high speed, and continue walking at a slightly faster pace. Repeat the above processes until the boss is dead – three rounds of this, or nine hits to the head.
After the battle, go to the bottom of the pit once more and charge up your sword for a Skyward Strike. Hit the sealing stone to banish the creatue for somewhat longer.
Afterwards, you’ll end up back in the Sealed Temple.