Midnight Cave: The Time Experiment UP103

In 1972, a French speleologist named Michel Siffre spent six months living in total isolation in a subterranean cave, without access to clock, calendar, or sun. Sleeping and eating only when his body told him to. His goal was to discover how the natural rhythms of human life would be affected by living “beyond time”.

Siffre was isolated in a large cave chamber 440-feet from the entrance. His furnishings were sparse: a tent erected on a wooden platform was equipped with a bed, table and chair, and various machines for science experiments. The chamber was also stocked with frozen food and almost 800 gallons of water.

In Midnight Cave, each one of Siffre's "days” involved a set morning routine. As soon as he awakened, he reached for the nearby telephone to let above-ground researchers know that he was awake. Immediately, lights controlled by the researchers were turned on, and Siffre began a four-hour regimen of experiments. First he took his blood pressure, then a series of mental, memory, and physical tests. He rode a stationary bicycle for three miles and used a pellet gun for five rounds of target practice. When he shaved, he collected his whiskers for experiments at the University of Minnesota.

During his free time, he swept the guano-filled cave, trying not to breath the dust which could cause him to develop a lung disease. He had planned to listen to music and read to fill the lonely hours. Unfortunately, the damp cave environment caused his stereo to malfunction and ever-present mildew to attack his books.
By the end of the first month, he was living a 26-hour cycle, though he didn't know it at the time. He simply stayed awake as long as he wanted and called it a "night" when he felt tired. He let the researchers know when he was ready to sleep, and the lights were turned off. He kept a diary that tracked his own days and nights, but his calculations were not accurate. For example, his Day 63 was really Day 77, aboveground.