Onigumo's cave

was a secret cave where the bandit, Onigumo was nursed by Kikyō before he fused with demons to become Naraku. The cave was set on fire a few days after Kikyō's death. Naraku's demonic aura still lingered in the cave 50 years after he was created. It was strong enough that not even grass grew where it permeated from.

When Onigumo was reborn as Musō, he had forgotten who he was. He ventured towards the cave where he began to remember his past.