Onimusha: Warlords/Underground temple

Once down the hole follow the path and 2 ninja genma will attack. In the next screen is an ornate entrance. To the left of the stares leading inside is a chest with the Und. Temple Map inside. Be careful when you approach the stairs since a ninja genma will jump down once you begin to scale them.

The shrine
Once inside there is a shrine with a mummified monk guarding a scroll. Take the green scroll and gain Sougen's Note. It gives more details on the ogre's gauntlet and opens a secret door. Past the door is a hallway filled with 4 soldier genma (2 in either direction). To the right is a dead end with a cupboard containing Seiryu. Backtrack and take the left hall that leads to a door. This room contains 6 breakable vases and a shrine holding the Thunder Orb. One of the vases hides a chest that contains Journal #1. After getting the journal go to the shrine and claim the Thunder Orb. Your sword can now turn into Shidan and use the magic spell Raizan.

To the left of the shrine is the next hallway. Down the hall is a trick treasure box. Continue up the stairs to exit the temple.

Outside
Once outside immediately in front of you hidden in the bushes is a chest holding a Magic Jewel. Continue down the trail until you reach another building. To the left of the entrance is a magic mirror and chest containing an encoded request. Since you only have 1 out of 4 books to use to encode it move on.

Since you found the Thunder Orb you can remove the barrier on the door and go through it.