Did you mean the Stargate SG-1 episode Avalon?

Avalon, a mythical place where Merlin placed a stone with a sword in it, to see if anyone with honour and intelligence could be worthy to take the treasure of all treasures. Cameron Mitchell, Daniel Jackson, Vala Mal Doran and Teal'c were pursuing this goal when finding out where this Avalon ought to be. Avalon is actually real and situated in UK under a hill, circa 125 miles northwest of London. Under that hill, Ancient devices protected a cavern where a holographic Merlin said that they were to be tested. They endured a two tests of their wisdom, while Mitchell fought a holographic guardian of a knight. After they succeeded, a great many treasures were revealed, including a book on Ancient history, as well as an intergalactic communication device. Merlin presumably named it after the Alteran name for Earth. (SG1: "Avalon")

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