After acquiring the Dungeon Map, 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 middle 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.
South Room (Again)
Return to the middle 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.
Heart Piece 17
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 Heart Piece 17.
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.