Consult this map for part 3:

Now exit and enter the main door and watch a cutscene. During the cutscene, you can see a treasure box, so pick up it after the cutscene is finished.

• Equipment: Normal Arrows

Now that there are 2 more doors, go to the right first (the one without magic seal). Inside is a journal file.

• File: Journal #3

Get out of the room, this time enter the sealed door with Enryuu. Two Three-Eyes will welcome you in this room, so you know what to do. Proceed to the next area. Well, another cutscene with a kid and your comrade Kaede. Notice the double doors sealed by green demon plates? remember it for now. Continue the hallway and enter the wooden door. There are a few Zombie Soldiers and a Three-Eyes, finish them off. Beneath the staircase is a door leading to a small room. Inside is a big trick box (NOTE: DO NOT randomly attack in this room or you will cut a robe). Do not go outside yet, there is another file on the shelf.

• Equipment: Bow (Solution: left, right, left, right, right)
• File: Suzaku

There is nothing else in this room, so you can get out now. Before you go upstairs, check out the treasure box in the corner for Herb. Above the treasure box is another hidden Fluorite.

• Item: Herb
• Item: Fluorite

Now go upstairs and enter the door right next to the staircase. Examine a bucket in the middle of the room for a Power Jewel. Remember I said not to cut the robe downstairs? :P

• Item: Power Jewel

Get out and continue, feel free kill monsters a long the way. Two doors here, go to the level-2 sealed door first. In the room, open a treasure box for R. Crest Piece and pick up a Red Book on the table.

• File: Red Book
• Key Item: R. Crest Piece

Exit the room. 
NOTE: Before you enter the double gray doors, change your weapon to Bow and Arrows because you will need to help 2 soldiers outside. You only have one a chance to help them because they will disappear if you re-enter. The reward for saving them is Herb and Magic Jewel. It's probably safer to go back and save the game to avoid missing these items. After saving them, wait until the items appear on the ground. Once you see the items flickering on the ground, you can go all the way back to pick them up.

• Item: Herb
• Magic Jewel

Back to the where you were, circle a little you will see another level 1 sealed door, open it. Kill all the demons inside, then advance to the next door. You'll notice an obvious crate, destroy it to reveal a Normal Arrows box. The corner beneath the staircase is another Fluorite. 

• Equipment: Normal Arrows
• Item: Fluorite

Now head upstairs. This room has a Magic Mirror, a treasure box, and a file (right next to the treasure box).

• File: Byakko
• Equipment: Normal Arrows
   

Now enhance your weapons and save your game. Open level-2 sealed door and watch a cutscene. From this area, you will have to solve 4 different traps in order to move forward.

First trap:

• Step 1: there is only one lever, pull it.
• Step 2: move Kaede to pull the right lever.
• Step 3: move Sam to pull another. It will open another section.
• Step 4: This section has 3 levers, move Kaede to pull the far left. This lever will also open the cell containing a treasure box.

Move Samanosuke to pick up the Holy Armor from the treasure box then equip it immediately.

• Equipment: Holy Armor

• Step 5: Move Samanosuke to pull the right lever (the 3rd one from Kaede).
• Step 6: Enter the door, you don't have to pull the last one.

Second Trap:

It's pitch black in this room, so lit all the candle with your fire sword (press triangle button) then advance to next door. 

Third Trap:

This one is easy too. Since the pattern is random, I won't be able to help you much, so just be careful not to kill each other or it will game over. The trick is that you don't have to move both of them to other side. The strategy here is to move Samanosuke forward and have Kaede stepping on the same 2 trick tiles. After you reach the circle tile, step on it to disable the trap.

Yey! you made it. But there is another one!!!

Fourth Trap:

Follow the images below:
 

You finally made it. Advance forward to the next door, then another door, you will see an obvious box on the wall with a string, pull it down to disable all traps that you just went through. You might want to go back to save your game at this point.