Cardiff Space-Time Rift

The Cardiff Space-Time Rift, known locally as the Rift, was a time rift situated in and above the city of Cardiff.

Geographic location
The Rift stretched about five mile miles from Cardiff Bay. (WEB: torchwood.org.uk) When the Rift fractured, it temporarily spread out from Cardiff to cover parts of the entire Earth, including London and Tokyo. (TV: End of Days)

According to Vox, the Rift had several openings across the Milky Way galaxy, which were presumably switched between randomly. (COMIC: Rift War!) This is supported by the fact that objects from all across time and space came through the Rift, ranging from dinosaurs and Bubonic plague from the past to alien objects from distant planets.

Prison of Abaddon
The Rift, in some way, acted as a prison for Abaddon. (TV: End of Days) In 92 AD, a Roman stationed near the future site of Cardiff had heard of legends of "a demonic giant trapped beneath the earth." (WEB: torchwood.org.uk)
 * The Disciples of the Light may possibly have created the prison, and likewise the rift itself. We do not know how long it has existed.

The Gelth's use of the Rift
Following the Last Great Time War, the Gelth fled to 1869 Cardiff through the Rift. They were able to take over the bodies of human corpses and tried to invade the planet and kill the entire species. During this attempt, the Rift was closed by a psychic named Gwyneth. (TV: The Unquiet Dead)

Torchwood Institute's interest in the Rift
Around the turn of the 20th century, the Torchwood Institute became aware of the Rift. In 1883, Queen Victoria herself spoke to the Institute on this subject, stressing the danger the Rift posed. (WEB: torchwood.org.uk) Agnes Havisham believed it was a threat and helped set up Torchwood Three to study it. (PROSE: Risk Assessment) Some time before 1913, they began work on the Rift Manipulator. (WEB: torchwood.org.uk)

Located in an underground base called the Hub and under the command of Captain Jack Harkness, Torchwood Three had the tasks of monitoring the Rift and phenomena associated with it and with securing for Torchwood any artefacts that came through. (TV: Everything Changes et al) The Hub also possessed a Rift manipulator which allowed them to control the Rift to a limited extent. (TV: Captain Jack Harkness, TV: End of Days)

The Widening of the Rift
The Rift was used in September 2006 by both the Ninth Doctor to power up the TARDIS, and by Blon Fel-Fotch. Blon Fel-Fotch, then mayor of Cardiff, built a nuclear power plant on the site of the Rift and plotted to cause a core meltdown. The meltdown would have destroyed the Earth, generating a shock wave that she could ride to escape off into space using a tribophysical waveform macro-kinetic extrapolator. The extrapolator, connected to the Doctor's TARDIS, accidentally widened the Rift and caused an event known as the Cardiff earthquake. (TV: Boom Town) Subsequent to that event, the width and activity of the Rift increased. (WEB: torchwood.org.uk)

Warning signs
As early as spring 1913, the Torchwood Institute had noted ground tremors and Rift activity. They theorised that an event which had not happened yet had sent a ripple effect back through time. The event, they predicted, would occur in the early 21st century. (WEB: torchwood.org.uk) In late 2007, increased numbers of Weevils coming through caused Jack Harkness to feel some concern over increased Rift activity. (TV: Everything Changes)

The event
In early 2008, Bilis Manger contrived to trick Torchwood Three's Owen Harper into using the Rift Manipulator to widen the Rift on purpose. This caused the Rift to fracture, resulting in time slips worldwide. Many believed the end of the world had come. (TV: Captain Jack Harkness, End of Days)

In Cardiff, more Weevils came through, as well as a Roman soldier and sufferers of Bubonic Plague. Finally, as Manger had planned, the Rift opened wide enough for Abaddon to escape. Jack stated that the area would become more active after the opening of the Rift and the death of Abaddon. (TV: End of Days)

Later uses and discoveries
Not long after Abaddon's defeat, the Tenth Doctor used the Rift to "fuel up" the TARDIS, commenting that the Rift had recently been active. (TV: Utopia)

The Rift caused an overlap in time between 1918 and 2008 in a Cardiff hospital, creating the illusion of "ghost sightings" in both times. Torchwood Three sent a cryogenically frozen soldier from 1918, Tommy Brockless, back from 2008 through a time hole with a "Rift key", and he was able to close the hole. (TV: To the Last Man)

The same year, Gwen Cooper discovered an unknown property of the Rift, that it abducted people from Cardiff as well as depositing creatures and objects from the other side. She found out that a number of missing people could be connected to the activity of the Rift. (TV: Adrift)

Jack Harkness's brother Gray, during the latter's revenge on Jack, forced John Hart to widen the Rift in order to create chaos around Cardiff. (TV: Exit Wounds)

Using the Rift positively in the year 2009, Gwen Cooper and Ianto Jones of Torchwood Three used the Rift Manipulator in conjunction with Sarah Jane Smith's supercomputer, Mr Smith, to power a message to the Doctor via Martha Jones' superphone. (TV: The Stolen Earth) They later used the combination of the Rift and Mr Smith again to help the Doctor return the Earth back to its regular orbit. (TV: Journey's End)

Closure
The Rift was finally closed when the House of the Dead, which was built on a crack in the Rift, was destroyed. (AUDIO: The House of the Dead)

Travel through the Rift
Beings and objects could be transported through the Rift. When the Rift became active, a Rift Storm, which acted as a portal through the Rift, would open up and beings and objects could cross through from one side to the other. (COMIC: Rift War!)

Some extraterrestrials were also known to be able to manipulate travel through the Rift, as the Weevils could use the Rift to cross into Cardiff, and the Sanctified were able to manipulate and open Rift Storms to transport their Harrowkind troops through the Rift. (COMIC: Rift War!)

Use by other extraterrestrials
The Weevils used the Rift to cross over into Cardiff for reasons of their own, more so as the Rift de-stabilised. (TV: Everything Changes, Combat, End of Days) The Sanctified Empire were also known to harvest energy from the Rift, and used it to send their Harrowkind troopers to their intended destinations. (COMIC: Rift War!)

Other aliens used the Rift, including Mary and her guard in 1812 and the "Sex Gas" in 2007. Perhaps coincidentally, they came to Earth close to the Rift, though apparently neither used it as their means of transport onto the planet. (TV: Day One, Greeks Bearing Gifts) A Dogon eye was also found near the Rift, though whether it came through the Rift is unknown. (TV: Random Shoes)

Indirect influence upon Cardiff
Individuals who lived near time fissures (TV: Image of the Fendahl), may have developed psychic powers, such as Gwyneth, who had the gift of clairvoyance. (TV: The Unquiet Dead)

Behind the scenes

 * There are two different sources on how the Rift closed. According to AUDIO: The House of the Dead, the Rift finally closed when the House of the Dead was destroyed. However, this is contradicted by Russell T Davies, who stated that the Rift closed with the Cracks in Time when the Eleventh Doctor rebooted the universe.