From time to time I play the easier ones of Shostakovitches Preludes and Fugues, but the B flat minor fugue I can hardly play the starting theme, certainly no further than the 'second' entry of the subject.
These wonderful pieces were written for Tatiana Nikolayeva. Whilst recitalling the whole series in New York she collapsed during the B Flat Minor Fugue, and died shortly afterwards. She recorded them twice, I prefer the later version on Hyperion. (Her Bach '48', on which Shost modelled his work is pretty good also)