The Pandorica was a prison hidden under Stonehenge. It was built to hold the Doctor and ensure the safety of the Alliance. Despite being described time and again as the "perfect prison" by the Eleventh Doctor, it also proved to be "easy" to open from the outside; Rory Williams, on instruction from the Doctor, opened it with the sonic screwdriver.
The Pandorica was actually a prison built by the Alliance for the Doctor to stop him from inadvertently destroying all of creation in every Universe. They believed 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 a form of escape. (TV: The Pandorica Opens)
After the Alliance trapped the Doctor in the Pandorica in 102 AD, the Auton duplicate of Rory Williams succumbed to his programming and shot Amy Pond. (TV: The Pandorica Opens) However, a future version of the Doctor was able to go back in time using River Song's vortex manipulator and tell Rory how he could use the sonic screwdriver to release the Doctor, as well as use the Pandorica to save Amy. By sealing the near-dead Amy inside the Pandorica, it was then kept shut until 1996, when her younger self in the new timeline where only Earth existed came to the museum where the Pandorica was kept on a school trip. Contact with the Pandorica gave it a sample of young Amy's DNA, which it could use as a sample to fully revive the nearly dead adult Amy. During this time, it was moved several times.
It was once put into storage in a London warehouse which was destroyed by the Blitz in 1941. It was reportedly seen being dragged to safety from the burning warehouse by the Last Centurion, and 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 piloted it into the exploding TARDIS which had cracked all of time and space. The atoms from the Pandorica combined with the energy of the TARDIS' explosion to restore every point in time and 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. (TV: The Big Bang)
As a "sneak preview", River mentioned to the Eleventh Doctor that he would see her again "quite soon. When the Pandorica opens." The Doctor responded that that was a fairy tale. (TV: Flesh and Stone) When Flemming was reading River's diary, he mentioned this adventure, remarking that it sounded "exciting". (TV: The Husbands of River Song)
The Pandorica looked like an image of Pandora's Box on a book found in Amy Pond's bedroom. It was lined with a very ornate and complex set of security tumblers that glowed green when they were being unlocked, likening the Pandorica to a heavily vaulted safe. (TV: The Pandorica Opens)
The interior was a small room with a chair in it and a set of manacles built into the arm rests. When someone was placed on the chair, the exterior would close and the manacles would lock around their wrists to shackle the person to the chair, sealing them in tightly. (TV: The Pandorica Opens)
The Eleventh Doctor was put in the chair by the Alliance to stop him from destroying the universe. Using the sonic screwdriver given to him by a future version of the Doctor, the Auton copy of Rory Williams opened the Pandorica and released him. (TV: The Pandorica Opens)
The Doctor and the Auton duplicate of Rory put Amy in the Pandorica while she was dying. 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. (TV: 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". The Alliance trapped the Doctor in it again and it was up to the guests to bring the TARDIS to him, so he could escape. The Doctor considered the Back Up Pandorica as cheating and complained on the fact that it wasn't even a different colour.