Sanctuary Base 6. (TV: The Impossible Planet)
A sanctuary base was a type of base, typically placed on planets by humans who wished to observe the planet. These bases were constructed using kits (TV: The Impossible Planet) and could be constructed in any environment. Any lifeforms could survive on hostile habitats using sanctuary bases.
Sanctuary Base 6 was established in Krop Tor and lost when the planet fell into a black hole in 4221. (TV: The Impossible Planet/The Satan Pit)