Underground day 4. br br In a room with a beautiful pond the astronauts enjoy a meal before descending even deeper into Earth. br br An international crew of six astronauts are training for 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. br br After a week of training they entered the caves to spend six days living and working underground.