Magician David Blaine's latest stunt is to spend 7 days underwater inside a huge sphere at the Lincoln Center for Performing Arts in New York.
During the seven-day challenge the water temperature will be maintained at around 36C and he will be able to control his own core body temperature by wearing specially designed wetsuits.
He has also undergone intensive training for the challenge, shedding 50lbs (23kg) in body weight since January to improve the efficiency with which his body uses oxygen.
"I feel pretty good. Though I've been sleeping very little and breath-holding non-stop," Blaine said.
"My system is completely empty and I did that so there's no waste. That way in the sphere I don't have to use the bathroom."