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 and Teal'c were pursuing this goal when finding out where this Avalon ought to be. Avalon is actually real and situated in Scotland under a hill. Under that hill, Ancient devices protected a cavern where a holographic Merlin said that they were to be tested. (SG1: Avalon, Part 1)

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