Veronique Le Guen, who for 111 days lived in dank underworld isolation, has been found dead in a car, an apparent suicide, police said Thursday.
The cave explorer was 33 and died of an apparent overdose of barbiturates.
Her body was discovered in a car in northeastern Paris, said police, who called the death a suicide. There was no indication how long she had been in the car.
Equipped with 264 gallons of water, 900 books and crates of canned and frozen foods, Le Guen descended into a limestone cavern 275 feet underground on Aug. 18, 1986, near Millau in southern France. She had volunteered to become a hermit living in solitude to test the effects of isolation on the human body.
Although she had spent several years exploring caves with her husband, Francis, she was not a scientist but an executive secretary, the daughter of shopkeepers in a Paris suburb.
As a child she was an avid reader who often asked her mother why she hadn't been born a boy. "She thought you had to be a boy to have adventure," said her mother shortly after she was brought out of the cavern.
She volunteered for the experiment at the urging of French cave researcher Michel Siffre, a friend of her husband who was nearly driven to madness after spending 205 days in a cave near Del Rio, Tex., in 1972.
She wore no watch and bore no other instrument to determine what time or day it was or what was taking place above ground. Her only contact was by telephone. An underground remote camera monitored her movements.
Observers on the surface monitoring her said that one "night" she slept for 31 hours. Another time, she took an afternoon "nap" that lasted 18 hours but when she awoke, she thought she had only been asleep a few minutes.
Finally, she settled into a rhythm of 20 hours asleep and 30 hours awake during the experiment.
"I didn't care if it was night or day. For me it was eternally night," she said later.
Originally, she had thought she would keep track of time through her menstrual cycles but instead of normal periods of 28 or 30 days, in isolation she discovered later that they dropped to 18 and then to 11.
Despite the changes in her biochemistry, she returned pale but healthy to the surface on Nov. 29, 1986, eclipsing a 20-year-old record for women set by Josie Laures, who had stayed underground for 88 days.
In a book on her experiences that was published last summer, "Alone at the Bottom of the Pit," she described the stress brought about by the long isolation and her fear of sleeping and "staying in hibernation."