Scenes from training of six astronauts who will spend six nights underground in a cave in Sardinia, Italy. After a week of training, the astronauts descend into the caves to set up basecamp 800 m underground.

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.

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 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.”

Follow the underground adventure on Twitter with @ESA_Caves, and on the CAVES blog.