The rock wall where Andy leaves directions and money for Red was made by hand. The art department built it several months before filming and left it exposed to the elements to make it look real. It needed to look weather-beaten before shooting.
The wall stood for several years until it was sold, you guessed it, on eBay, by the farmer who owned the land. The tree is still there, although it was struck by lightning in 2011. Die-hard fans can still see parts of the wall on the grounds of the Ohio State Reformatory.
A Different Ending
Frank Darabont didn't want to show Andy and Red's reunion at the end of the film. Apparently, he wanted the final scene to show Red getting on the bus ride and going off into the sunset, and presumably, in the direction of the field Andy talked about during the whole movie.
The execs at Castle Rock had a different point of view, that of pleasing audiences with a happy ending. The ending we got was a compromise. We see the two reunite on a beach, but from a distance.
Changing the Filming Location
As mentioned previously, the movie ends with Andy and Red reuniting on a beach in Zihuatanejo, Mexico, in 1966. At that time, Zihuatanejo was just a small fishing village, but 28 years later, when the movie was being shot, it had become a vibrant tourist destination and not a deserted paradise as we see in the film.
The beach that we see at the end of 'The Shawshank Redemption' is actually in the Virgin Islands.
Shawshank and 'The Count Of Monte Cristo'
'The Shawshank Redemption' is very similar to 'The Count of Monte Cristo'. Alexandre Dumas' novel is even mentioned in the film. The story's protagonist is put in jail for a crime he didn't commit (check). He later escapes through a tunnel that took him years to complete.
After his escape, he finds buried treasure that he heard about in jail and uses it to get revenge. The "Count" is essentially Andy and Red rolled into one, plus a thirst for vengeance.
There are Many Wardens in the Novel
One way the film differs from Stephen King's novella is that the book features multiple wardens during Andy's time in prison. That's why Warden Norton, in the movie, seems to have multiple personalities because, in a way, he does.
One day, Norton is kind to Andy, allows him to send letters, and lets him work in the library. On another, he is an entirely different person who treats Andy disgustingly. The wardens in the books (the good and the bad ones) were rolled into one (seemingly) schizophrenic character: Warden Norton.