EXCLUSIVE

"Ghost Adventures" host Zak Bagans has taken on his most terrifying project yet -- he just bought a house in Indiana ... believed to be the site of one of the most terrifying demonic possessions ever ... a rumored "portal to hell."

The house rose to fame in 2012 ... after a mother who lived there reported her 12-year-old daughter and 9-year-old son had been possessed. Shockingly, there are even docs from child protective services that back up her claims.

Among the many scary incidents ... the mother says she witnessed her daughter levitating above her bed.

She also said she saw her son walking on their ceiling ... an account corroborated by several other witnesses. The mother did everything she could to de-demonize the house -- including building an altar and hiring an exorcist -- but nothing worked and she eventually moved.

Zak tells us, he caught wind of the horrifying tale and made an offer to purchase the home for $35,000 -- the owner was all too willing to sell.

The photo shown above is an actual police photo of the house ... and it's hard to miss what looks like an apparition in the window.

Zak says he's going to live there and document his experience -- "If it's true this home is a portal to hell, then I want to go there and see what happens."

Balls of steel.