Which Doctor Who episode, first broadcast in 2010, introduced the mysterious Pandorica?

The Doctor Who episode first broadcast in 2010 that introduced the mysterious Pandorica was The Pandorica Opens.

It is the twelfth episode of Doctor Who’s fifth series and was written by Steven Moffat. Matt Smith plays the Eleventh Doctor, with Karen Gillan as Amy Pond and Arthur Darvill as Rory Williams. The episode builds toward the discovery of the Pandorica, a legendary prison whose contents are initially unknown.

The title alludes to Pandora’s box, but the Pandorica is a distinct science-fiction invention rather than the jar from Greek mythology. The episode uses the idea of an apparently sealed container holding a dangerous secret and turns it into a major mystery within the Doctor’s wider story.

The story concludes in “The Big Bang,” the following episode. Viewers sometimes combine the two titles because they form a two-part finale, but the Pandorica is introduced in “The Pandorica Opens.”