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3: The number of years Italian sociologist Maurizio Montalbini, 53, plans to spend locked away in a dark underground cave as part of a study into the body's natural cycles.
80: The depth underground, in metres, of Mr. Montalbini's cave. It is two metres (6.6 feet) wide, 50 mtres (164 feet) long and five metres (16.4 feet) high.
9-10: Degrees Centigrade (48-50 degrees Fahrenheit), the temperature of Mr. Montalbini's cave.
4: Kilograms of honey, one of the food treats that will help Mr. Montalbini though his 3 year subterranean sojurn. Other treats include 2 kilograms (4.4 pounds) of nuts and 1.5 kilograms (3.3 pounds) of chocolate. His main diet will consist of food pills such as those used by astronauts.
85: Books in Mr. Montalbini's underground library. Although he will be spending most of his time in the dark, he has allowed himself the luxury of a few minutes reading each day by the light of a gas lamp.
366: The world record - also held by Mr. Montalbini - for the longest period of time, in days, spent alone in an underground grotto. It was set in 1992-3.
219: The number of days that Mr. Montalbini believed had passed during his record-breaking 366 days underground. One of the mysteries he is seeking to address in his latest experiment is why people who are shut away in the dark have longer daily cycles.
25: The number of hours at a stretch that another underground hermit, 27-year old Italian interior decorator Stefania Folini, stayed awake during her 130-day stay in a cave in 1989.
701: Length, in metres, of the world's largest cave chamber, Lubang Nasib Bagus ("Good Luck Cave") in Sarawak, Malaysia. The chamber is 451 metres (1480 feet) wide and 70 metres (230 feet) high.
20: Years that St. Anthony, the most famous Christian hermit, lived in complete seclusion at Pispir in Egypt in the 3rd Century AD.
Me time: Maurizio Montalbini plans to spend three years in a cave by himself