Underground day 5.

The astronauts continue testing a communications system before heading out for the last day of exploration. In a “grandiose finale” they discover a new series of caves.
An international crew of six astronauts trained on a caving adventure designed to prepare them for spaceflight. There are many similarities to spaceflight such as a lack of day--night cycle, sensory deprivation, minimal hygiene and the necessity to work as a team and solve problems together.
 
After a week of training they entered the caves to spend six days living and working underground.