Flat Holm
Flat Holm Island was located South-South-East of Cardiff Bay in the middle of the Bristol Channel.
Assumed to be just uninhabited scrubland, the island was secretly used by Jack Harkness to care for and keep safe, those who were taken in by the the Rift and who were returned, though scarred mentally (and sometimes physically). When he took over Torchwood 3 in 2000, Jack found two survivors in the vaults, so he created a building in which they could be cared for, calling them experiments which had gone wrong to the carers. Jonah Bevan eventually ended up there, as Gwen Cooper discovered. Jack had kept the existence of the facility secret from her. (TW: Adrift)