Cardiff Bay was the district of Cardiff where Roald Dahl Plass and the Hub, the base of Torchwood Three, were located. The Rift was located above it. The name "Cardiff Bay" was used to refer to both Cardiff's waterfront and the adjacent area of the Bristol Channel.
Torchwood Three also possessed a secret dock leading into Cardiff Bay which, until 2009, contained a small ship called the Sea Queen. (AUDIO: The Sin Eaters) The Sea Queen was replaced by the Sea Queen II. There was also a submarine, but it had been lost between 1970 and 2009. (PROSE: Risk Assessment)
In 2009, during the invasion of Earth by the New Dalek Empire, a Dalek saucer was sent to the Cardiff Bay to exterminate Torchwood Three, depositing a single Dalek which was prevented from entering the Hub by a time lock and subsequently destroyed when the New Dalek Empire was wiped out by the Meta-Crisis Tenth Doctor. (TV: The Stolen Earth / Journey's End) Later that year, the British government set off a bomb inside Jack Harkness' body in an attempt to (permanently) kill him. This destroyed the Hub. News media subsequently reported the attack as a bombing of Cardiff Bay. (TV: Children of Earth: Day Two)