About five years ago, when traveling, I first heard "Spiegel im Spieigel". Perhaps you will know it but I didn't then.
Back home I learned it is by Arvo Pärt, a composer from Estonia. It is a minimalist piece, for solo piano and violin. Its peace and tranquility have made it famous. I listen to it most days.
It was featured in BBC 4 Radio program "Download this audio clip.Audio player: p02qhsdc.mp3". I find the episode very moving.