I first visited the Cyclorama at Gettysburg during a family visit to the battlefield in grade school.  At the time, I remember the narration and shifting lights which guided viewers through the different points of action told through the painting (42 ft high and 377 feet long!).  Of course, we also visited the civil war battlefield itself, and the comparison between the real site of the battle and the representation was already apparent.

Visiting the Cyclorama again last spring in 2014, I noticed a number of changes in the museum (open again after a significant renovation since 2005).  Similar to a diorama, the painting is meant to draw viewers in and reveal aspects of the historical battle.  When the lighting dimmed, this sense of disbelief was also softened.