I found a clip on YouTube of the opening scene from Amadeus at the National in 1979.

https://www.youtube.com/watch?v=rvPIjzp9NPc

It finishes just seconds before one of the most theatrical moments I can recall. Paul Scofield as Salieri turned anticlockwise through a three-quarter circle, with his back for a second to the audience. He started the move as he is at the end of the clip, old and angry and alone on stage. When he finished the pirouette he was back in the past he'd been describing, his hand was out affably greeting two actors in his drawing room, his back straight, he seemed inches taller and he'd thrown off forty years. It was an astonishing piece of theatre. I can think of few actors who were his equal.