After entering and regaining control, use the nearby Bird Statue to save, then follow the path downstairs. As you go down, you'll encounter a few spider webs; you'll need to cut them down, as well as the Keese and trees in the area. At the end of the path, you'll find another grouping of trees. Cut them down and back up some.
On the ledge above, there is a Deku Baba (a species of carnivorous plant that are famous for their short temper & feisty attitude) and if you take the more obvious method, you are going to get hurt. So, as I said, back up and shoot at the crystal switch with the Slingshot and the door nearby should open up. Go in there.
Go up the nearby staircase to a higher central platform. As you do, an eye will open above the northern locked door. Withdraw your Goddess Sword. Seeing as the eye will follow your blade's tip (remind you of the Mr. I (or whatever it was) from Super Mario 64?), you can move your sword in a circle a few times. The eye will redden and die, also opening up the door. Go through the next room.
Here, you'll find some Deku Babas hanging from the roof, as well as some spiky enemies in the grass, if I recall correctly. Defeat the enemies and proceed forward to the bulk of the room, where you'll find a Bird Statue. Save, then do a 180 and shoot down the spiders (Walltulas) on the walls. Climb up these vines to the alcove above, where you can cut down the boards here for a future shortcut. Return to the previous room.
Go to the central portion of the room and slice up the Bokoblin there. The three doors here are locked; look at the eastern one and up to find a crystal switch. Shoot it to open the door and go through.
In here, proceed forward and cut down the spider web. Drop the lower area of the room further ahead and examine the eastern wall (remember, my directions are usually MAP-based) for a bit. Once you find the tunnel, crawl through to the statue and shoot the crystal switch it is "holding" to fill up the rooms with a bit of water. Swim over to the vine curtain nearby and go up. Enter the tunnel and exit into the previous room, then continue to the central of the rooms.
Here, go towards the western door. It is still locked. However, we now can UN-lock it. Get into the water and swim beneath the bridge connecting the central platform with the western door. Nearby should be a crystal switch. Get onto the platform and hit it, thereby opening the western door. Swim out from under the archway, ascend the vines, and go through the newly-opened doorway.
In this room, you'll find two Skulltulas hanging from their vines on the main bridge. Trust me when I say you will not want to cut these webs down - these Skulltulas can become a huge pain, and rather scary as they can get tough to defeat off of the webs.
Head to the western side of the room (map-based - I have to drill that into you!) and look up. You'll find two curled-up vines; shoot them BOTH with the Slingshot to make them usable. Use them to go across the gap safely. On the other side, defeat the Quadro-Baba and ascend the nearby stairway. Go through the door.
Go up this path to find a chest, in which you'll find the Dungeon Map. Now, go back to the previous room. Here, notice you're behind the Skulltulas, as in "their soft, weak underbellies are exposed to attack". And so they are.
Go to them and target-and-thrust your sword twice into that weak point to defeat them, cutting down the impeding webs as you go. Afterwards, cross the bridge, examining the western wall. You'll find a crystal switch; strike it with the Slingshot to flood this and the central room. Go through the northern door to the central room.
Next, head over to the east-central(ish) side of the room. Nearby, a log should be floating in the water. Above it are some vines, on which are some Walltulas. Shoot them down, then jump onto the log and the vines. Climb the vines and get onto the nearby ledge. Go into the room nearby.
In here, go downstairs to find a Skulltula hanging from a web. How are you to deal with this one? Hit it with a horizontal slice (Skyward Strike if you fear being hit) and the Skulltula should expose its purple spot. Thrust your sword into it to damage it. Repeat to kill it.
Now, examine the northern wall here. Back up some from the bars and an eye should open. Move around until BOTH of the eyes on the wall are open, then move your sword tip in a circle to kill the eyes, thereby letting you open up the chest, which contains a Small Key .
Return to the central room and go across to the northern door. Shoot down the Amber Relic from the south side and grab it, then insert the Small Key into the door and go on through.
And so, we arrive in another large room. We'll be doing some looting and wanton murder in a bit; for now, face the large central structure and use the slingshot to open the door into it. Go inside to find and battle a Stalfos. To put it roughly, just treat it like a high-power Bokoblin.
After the battle, open the chest to get a Beetle. This magnificent flying device can grab items for you, hit switches, cut wires and ropes, and even cut down hanging Deku/Quadro Babas! Since the room is still locked, launch the Beetle up high and through an opening near the top. After going through the web, go to the right and hit the crystal switch above the door to unlock it.
Exit the room and you can explore the area. Use the Beetle to explore many of the higher tunnels and cut down boxes; you'll find quite a few Rupees overall! Once you're finished, go to the west side of the room and use the Bird Statue. Go to the northern end and turn around to find a Piece of Heart behind some bars.
Use the Beetle to fly up to a hidden opening and hit the switch to open the gate, letting you obtain the Piece of Heart. Return to the aforementioned Bird Statue and launch the Beetle into the tunnels above the door. Cut down the Deku Babas and hit the switch. Go through the newly-unlocked door.
Here, just go straight to the other door at the opposite side of the room. Inside this room, the door will lock behind you. Go forward and a Skulltula will drop down. Hit it with a down-up vertical slash, then a fatal blow to finish it. Turn around afterwards and ascend the vines to reach the ledge. There, push the nearby box to the lower area.
Go there yourself and pull/push it eight spaces west and north to put it in the center of the room. Stand atop the box and withdraw your sword and the eyes (three of them) should be open. Do a few circles to kill the eyes and allow you to receive the Small Key from the nearby chest.
Return to the previous room. Launch your Beetle and send it to the higher ledge nearby, through the Skulltula web, and hit the crystal switch, thereby flooding this room with more water. Go up the nearby partial staircase and defeat the Skulltula if you want. Proceed to the highest point in the room and cut down the trees, then crawl through the newly-found tunnel. After exiting, go back to the extra-large room.
Next up, head over to the opposite (eastern) side of the room. Here, you'll find a tightrope. Don't yet cross it, though. Use your Beetle to cut down the Deku Babas hanging from the roof, THEN walk across the rope. At the other side, use the Small Key and go through the door.
In here, simply go along the path and cut down any impeding wooden boards. You'll soon come across the three-headed Staldra. You are to hit all three of its heads nearly-simultaneously; otherwise, it won't die. I prefer to kill one head first, then, when the heads regrow and line up for a second, go a Spin Attack.
Go through the newly-opened door and defeat the Bokoblin you'll find further along the pathway. Go further along to the Skulltula over an abyss; defeat it by using the Beetle to cut down its web. Then dash-jump across the abyss and you'll find a gate to the left. Above it, you'll find a crystal switch; hit it with the Beetle or the Slingshot (the former saves Deku Nuts).
Okay, after that, you'll probably notice the huge abyss and the Bokoblin on the other side of the tightrope. Start climb along it and, soon enough, the Bokoblin will start to go towards you. Be sure to jostle it off the rope when possible, then get on the other side of the abyss. There, use the Bird Statue and go into the western room. Open the chest for a Red Rupee, then go into the eastern room and ascend the vines.
On the upper ledge, cut the rope and dash for the now-swinging rope. Press and hold B to stop swinging, then face to the right. Swing towards that vine-covered platform. Climb the vines on the central platform and walk along the path. At its end, shoot down the two curled-up vines above you with the Slingshot (or the Beetle).
Jump onto one vine, swing to the next, do a nice Tarzan yell, and land on the ledge to find a chest, in which is the Golden Carving . This golden item fits in the large gold lock across the abyss, and functions much like the Boss Keys of Wind Waker (a previous Zelda).
Ascend the vine and jump across the top area to return to the southern portion of the room. Once again, cross the tightrope and utilize the Bird Statue. Examine the large door and you'll have to fit the Golden Carving into the door.
To do so, use the Wii Remote with the A button held to rotate it, the C button to reset this, and Z to view the lock. When you line it up and are not holding Z, press A to insert the Golden Carving, opening the door, and bringing you in to the room. After a lengthy scene, you'll fight your first real boss.
Boss: Demon Lord Ghirahim
In the initial part of the battle, Ghirahim will simply walk towards you. He comes with one hand raised upward, glowing red. The purpose of this is to grab your sword when you slice at him. If he DOES grab your sword, do a down-up vertical slice, or he'll steal the sword. During this time, he also can slap you if you take too long to hit. How do you hit him? Well, you need to lead his hand in one way, then quickly swing in a different way.
During this time, if he does manage to steal away your sword, you have two options. You can run around until he throws your sword at you, at which point you can grab it, or you can shield bash him during a slice.
Continue attacking for a while, after which this will change a bit. In the second half of the battle, Ghirahim will use his sword and will use three attacks. One involves teleporting and slashing at you (kind of like Sephiroth in Kingdom Hearts). Another involves a running tackle-slash combo, and another has Ghirahim launching five red projectiles at you.
For the first attack, just jump around, preferably backwards (because he'll appear from behind, and his position is apparently determined upon actually teleporting). For the second, shield bash Ghirahim to stun him and get a few hits in, or swing at him on the side his sword isn't on. For the third, dodge to the side or move your sword in a slash that would reflect as many projectiles as possible.
Eventually, the battle will end and you will have hopefully won. After regaining control of Link, grab the nearby Heart Container and take the door nearby to the Skyview Spring.