Pandorica

The Pandorica was a prison hidden under Stonehenge. It was constructed to ensure the safety of The Alliance and to hold the most feared being in the history of the Universe, which turned out to be the Doctor.

History
It was mentioned by Prisoner Zero to the Eleventh Doctor, who told him it would open and silence would fall. (DW: The Eleventh Hour) River Song also mentioned the Pandorica to the Doctor, telling him she would next see him there and that she remembered it well. The Doctor believed the Pandorica was a fairy tale (DW: Flesh and Stone). He later told Amy that according to legend, the Pandorica was the prison of a warrior or goblin who dropped out of the sky and tore your world apart until a good wizard tricked it and locked it up. (DW: The Pandorica Opens)

The Pandorica turned out to be a prison built by the Alliance for the Doctor to stop him from destroying all the universes. Their analysis held that the Doctor would be responsible for the destruction of existence itself. They used the lure of the Pandorica to trap him. There were many layers of security in the Pandorica including deadlocks, time stops and matter lines. It even had a restoration field to stop the Doctor from dying, which the Alliance believed to be a form of escape. (DW: The Pandorica Opens)

It was used to save Amy Pond. She was locked inside it for eighteen hundred ninety-four years until revived by her younger self. Her DNA provided the Pandorica the material it needed to fully revive the nearly dead adult Amy. During this time, it was moved several times.
 * 118 - Taken back to Rome under armed guard.
 * 420 - Plundered by the Franks.
 * 1120 - Prized possession of the Knights Templar.
 * 1231 - Donated to the Vatican.
 * Post 1231 - Sold by Marco Polo.

At an undisclosed time it was put into storage in a London warehouse, which was destroyed by the Blitz in 1941. It was found a short distance away, unscathed.

The Pandorica was also used by the Doctor to restore the universe. Since all of the traps inside it provided the perfect barrier against the destruction of the universe, it retained several billion atoms of the original universe within, even after the destruction of the rest of creation. Operating on the same principle as cloning a body from a single cell, these atoms provided a 'blueprint' for the universe when the Doctor threw it into the exploding TARDIS which had cracked all of time and space. The atoms from the Pandorica combined with the explosion energy from the TARDIS to restore every point in time and the rest of the universe. Doing so caused the cracks in time to close and allowed Amy to remember her family and the Doctor -- all erased by the cracks -- back into existence. (DW: The Big Bang)

Exterior
The Pandorica looked much like an image of Pandora's Box found in the bedroom of Amy Pond. Since they used her memories to lure the Doctor there, the Alliance probably designed it to look like this.

Interior
The interior was a small room with a chair in it. When someone was placed on the chair, the exterior would close, sealing them in. Many forms of security would stop the prisoner escaping.

Known inhabitants
The Doctor was put in the chair by the Alliance to stop him from destroying the universe. Using the Doctor's sonic screwdriver given to him by a future version of the Doctor, the Auton copy of Rory Williams opened the Pandorica and released him. (DW: The Pandorica Opens)

Amy Pond was put in the Pandorica by the Doctor and the Auton duplicate of Rory after being killed. The imprisonment was meant to bring her back to life and she was restored when her seven-year-old self touched the box, causing it to open. Using its restoration field, the Pandorica resurrected the older Amy after it got a DNA sample from the young Amelia. (DW: The Big Bang)

Behind the scenes

 * For the Doctor Who Experience (London/Cardiff) part of the interactive story featured a device called the "Pandorica II" as part of its storyline.