Let's Go to Golgotha! is a 1975 science fiction story by Garry Kilworth, published in a collection of the same name.
In the future period where the story takes place, time travel has been invented and made commercially available. Among other historical events, tourists can book a time-traveling "Crucifixion Tour." Before setting out, the tourists are strictly warned that they must not do anything to disrupt history. Specifically, when the crowd is asked whether Jesus or Barabbas should be spared, they must all join the call "Give us Barabbas!". (A priest absolves them from any guilt for so doing). However, when the moment comes, the protagonist suddenly realizes that the crowd condemning Jesus to the cross is composed entirely of tourists from the future, and that no actual Jewish Jerusalemites of 33 AD are present at all.