The actual beach is not totally surrounded and enclosed by mountains, hiding it from the sea. In fact, there is a large gap between two gigantic boulders, and the films editors superimposed a fake mountain there in post-production.
Ewan McGregor was Danny Boyle's first choice to play the part of Richard. The studio wanted Leonardo DiCaprio and cast him before Boyle could intervene. While McGregor blames the studio, he has reportedly not spoken to Boyle since.
During the filming of the movie the film crew remodeled and flattened the beach using a tractor, making it unstable. The Boxing Day Tsunami of 2004 allowed the beach to be naturally restored to its previous state, much to the relief of the locals.