Cardiff Space-Time Rift

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

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. (TW: End of Days)

The location of the other end of the rift, on the other hand, was more vague. Objects from across time and space were picked up, ranging from a Pteranodon from the past to alien objects from distant planets. It was believed that the opposite end of the rift was either wandering in time and space or had several fixed openings which were switched between randomly. (WEB: torchwood.org.uk)

Prison of Abaddon
The Rift, in some way, acted as a prison for Abaddon. However, unlike the Beast, Abaddon could easily be freed if his particular trap was opened. (TW: End of Days)

In A.D. 92, 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 in order to use the rift. The Gelth had used the Rift to try and take over the bodies of human corpses and then eventually attempt to invade the planet and kill the entire species. During this attempt, the rift was closed by a psychic named Gwyneth. (DW: The Unquiet Dead)

Torchwood Institute's interest in the Rift
Sometime between the Torchwood Institute's formation in 1879 (DW: Tooth and Claw) and 1883, it realized the existence of the Rift. In 1883, Queen Victoria herself spoke to the Institute on this subject, stressing the danger the Rift posed. Torchwood found themselves unable to effectively get through the Rift, but decided to try to monitor it and secure whatever useful items might pass through it into Cardiff. Some time before 1913, they began work on the Rift Manipulator. (WEB: torchwood.org.uk)

The Widening of the Rift
The Rift was later used in September 2006 by both the Ninth Doctor to power up the TARDIS, and by Blon Fel-Fotch. Blon Fel-Fotch, now 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. (DW: Boom Town) Subsequent to that event, the width and activity of the Rift increased. (WEB: torchwood.org.uk)

Torchwood 3 and the Hub
At an unknown time, the Torchwood Institute set up a Welsh branch, Torchwood 3, though Queen Victoria knew of the Rift, the reason for the branch, in 1883.

Located in an underground base called the Hub and under the command of Captain Jack Harkness, Torchwood 3, had the task of monitoring the Rift and phenomena associated with it and with securing for Torchwood any artifacts that might come through. (TW: Everything Changes et al) The Hub also possessed a Rift manipulator (TW: Captain Jack Harkness, TW: End of Days).

Warning signs
As early as spring 1913, the Torchwood Institute had noted ground tremors and Rift activity. They theorized 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. (TW: Everything Changes)

The event
In early 2008, Bilis Manger contrived to trick Torchwood 3's Owen Harper into using the Rift Manipulator to widen the Rift on purpose. This caused the Rift to fracture, causing time slips worldwide. Many believed the end of the world had come. (TW: Captain Jack Harkness, End of Days)

In Cardiff more Weevils came through and onto the street, a Roman soldier and sufferers of Bubonic Plague, appeared. Finally, as Manger had planned, the Rift opened up wide enough to release Abaddon. (TW: End of Days)

Jack stated that the area would become more active after the opening of the rift and the death of Abaddon. (TW: End of Days)

Later uses and discoveries
Not long after Abbadon's defeat, the Tenth Doctor used the Rift to "fuel up" the TARDIS, commenting that the rift had recently been active. (DW: 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. By sending a cyrogenically frozen soldier from 1918 back through a time hole with a "Rift key" he was able to close the hole. (TW: To the Last Man) The same year, Gwen Cooper discovered an unknown property of the Rift, that it abducted people as well as depositing them, and she found out that a number of missing people could be connected to the activity of the Rift. (TW: Adrift)

Jack Harkness's brother Gray had John Hart widen the rift to create chaos around Cardiff. (TW: Exit Wounds)

Using the Rift positively in the year 2009, Gwen Cooper and Ianto Jones of Torchwood 3 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. (DW: 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. (DW: Journey's End)

Closure
According to Russell T. Davies, the Doctor's closing of the cracks in time also closed the Cardiff Rift. (DW: The Big Bang).

Use by other extraterrestrials
The Weevils used a Raft to cross over into Cardiff for reasons of their own, more so as the Rift de-stabilised. (TW: Everything Changes, Combat, End of Days)

Other aliens did use the rift such as 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. A Dogon eye was also found near the rift, though whether it came through the rift is unknown. (TW:Day One, Greeks Bearing Gifts, Random Shoes)

Indirect influence upon Cardiff
Individuals who lived near time fissure's (DW: Image of the Fendahl), may have developed psychic powers, such as Gwyneth, who had the gift of clairvoyance. (DW: The Unquiet Dead)
 * This may also account for the abilities possessed by Bilis Manger.