An international team of six astronauts from China, Japan, USA, Spain and Russia have descended into the caves of Sardinia, Italy, to explore the depths and train for life in outer space. One of the last unexplored environments on our planet, caves offer parallels to exploring space. ESA's underground training course "Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills" - CAVES - prepares astronauts over two weeks to work safely and effectively in multicultural teams.

After a week of training, the astronauts are now descending into the caves to set up basecamp 800 m underground.

The similarities between caving and spaceflight are highlighted throughout the course. Speleologists and astronauts adopt the 'buddy system', and both astronaut trainers and CAVES instructors repeat the same mantras of "slow is fast," "check your gear, and then trust it," and "always be aware of where you are and where your buddy is."

In every expedition, the astronauts work with seasoned instructors and explorers. "A mutual trust builds as stories and anecdotes are shared," says mission director Loredana Bessone. "The atmosphere is always one of respect."

CAVES focuses on multicultural approaches to leadership, following orders, teamwork and decision-making. At the end of the course the astronauts will have a better understanding of how they function in a multicultural team and what they are skilled at, as well as areas for self-improvement.

Behavioural activities are woven into the course to foster effective communication, decision-making, problem-solving, leadership and team dynamics.

"From the first activity together, the support team saw that this year's 'cavenauts' would be a really tight crew," says Loredana. "Their teamwork is an example of what an expedition in an isolated, risky and alien environment should be."

This year's participants are an even more international team than ever, including ESA's Pedro Duque, NASA's Jessica Meir and Richard Arnold, Japan's astronaut Aki Hoshide, China's Ye Guangfu and Russia's Sergei Korsakov.

The cavenauts bring a broad mix of skills with their backgrounds in science, engineering, flying, military and education as well as experience and culture.

Pedro Duque comments, "It is a great privilege to take part in one of the last exploration activities remaining on Earth and to enter the underworld supervised by world-class experts.

"We will use the knowledge we gain about ourselves and the group in our next space endeavours."

Follow the underground adventure on Twitter with via @ESA_CAVES, and on the CAVES blog where the crew have provided impressions of their first week of training.

Loredana concludes: "ESA's CAVES course brings together spacefarers from all over the world to create the best crew. We hope to see them one day exploring other worlds with the same awe and respect we have for caves."

CAVES: Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills