Gueorguiev, a motivational speaker and charity ambassador, has run some 30 ultra-marathons worldwide, from the Arctic to Cambodia, as well as a 217km race in California’s Death Valley.

“I want to challenge myself,” Gueorguiev told Reuters. “I want to show when you put someone in the box how psychologically they change.”

The funds raised will be used for various projects to prevent addictions among children under 18, including drugs, alcohol, digital media and energy drinks.

A box with three glass walls has been put on a pedestal in front of the National Palace of Culture in Sofia. Gueorguiev, who began his experiment today, will have a bed and a treadmill and no access to books, a computer or phone, only speaking to members of the public for 30 minutes every day.

“This is not a physical experiment it is psychological experiment,” he said.

In 2019 Gueorguiev ran 1,200km through Bulgaria, North Macedonia and Albania to urge governments to build better infrastructure to connect people.

In 2003, American illusionist David Blaine spent 44 days sealed in a transparent box suspended over the bank of the River Thames in London with only water to drink, in a stunt criticised by media and the public at the time.