John Edwards from the charity Walking Free was buried in an eight foot box on Friday to raise awareness of the difficulties faced by those with addiction and suicidal thoughts.
He's used his time underground to speak to those who wanted to talk about their problems.
Speaking to Premier from the coffin, he said: "It's been constantly suicidal people, gangsters, drug addicts, their mothers and fathers phoning in.
"We've bringing words of life from the grave to these people.
"Encouraging people, praying for people, it's been quite draining."
While admitting the challenge was as hard as expected, John explained that the conversations he's had and the publicity he's received have made it worth it.
"It's been far above and beyond my expectations of the influence that this has had all over the world, he said. "It's gone viral on social media and we've had different media networks on to us."
John will come back above ground on Monday evening.
You can watch a live stream from inside the coffin here:
Listen to John Edwards speaking to Premier's Aaron James here: