The remote Antarctic base Concordia.
ESA sponsors a medical research doctor in Concordia every winter to study the long-term effects of isolation.
The base is 3200 m above sea level and temperatures drop to –80°C. No supplies can be delivered during the Antarctic winter and nobody can leave the base, no matter what emergency.
The station is the closest thing on Earth to interplanetary exploration. Studying the effects of isolation there is preparing ESA for the real thing: a mission to Mars.