The Chamber of Life was a cavern created by the Great Beings to house the Kanohi Ignika. It sat at the bottom of a staircase of 777 steps and had multiple guardians.
The Chamber of Life was a secret chamber beneath Mount Valmai where the Mask of Life was kept hidden. It was guarded by Axonn, Brutaka, and Umbra. It could be reached by going through a hidden entrance in the Green Belt and descending a staircase with 777 stairs.
The Chamber of Life was not actually inside Mount Valmai, but rather underneath it.
The Chamber of Life was not directly underneath Mount Valmai.