Fifteen people endured more that a month without daylight, clocks or external communications to see how it would affect their sense of time.
The group, led by French-Swiss explorer Christian Clot appeared at around 10:30 am (0830 GMT) from the Lombrives cave in Ariege.
They lived in and explored the cave as part of a project called Deep Time, where there was no natural light, the temperature was 10C and the relative humidity 100 per cent.
Members had to generate their own electricity with a pedal bike and draw water from a well 45 metres below the earth.
The volunteers, aged between 27 and 50, had no contact with the outside world.
“It was like pressing pause,” said Marina Lançon, one of seven women to take part in the experiment.
According to the Guardian, Ms Lançon said she did not feel any rush to do anything and wished she could have stayed in the cave a few days longer.
She added that she was happy to feel the wind and hear birdsong again.
In partnership with laboratories in France and Switzerland, scientists at the Human Adaption Institue, monitored the 15 team members’ sleep patterns, social interactions and behavioural reactions via sensors.
One sensor was a tiny thermometer inside a capsule that participants consumed like a pill.
It analysed body temperature and transmitted data to a computer until it was ejected naturally.
The team members followed their biological clocks to indicate when to wake up, go to sleep and eat.
They counted their days not in hours but in sleep cycles.
“For us it was a real surprise,” the project director, Mr Clot, said. “In our heads, we had walked into the cave 30 days ago.”
One team member thought the time they spent underground was 23 days.
Two-thirds of the participants stated a desire to stay underground a little longer to finish group projects started during their stay, according to Benoit Mauvieux, a chronobiologist involved in the research.
The scientists said the £860,000 (€1.2m) project will help them better understand how people adapt to extreme changes in living conditions and environments.
“Our future as humans on this planet will evolve,” Mr Clot said after emerging.
“We must learn to better understand how our brains are capable of finding new solutions, whatever the situation.”