Daniel Barenboim performing the Beethoven piano sonata no. 28, opus 101. This was the favorite Beethoven piano sonata of the composer Richard Wagner.
The Piano Sonata No. 28, Op. 101 is the second of the series of Beethoven's "Late Period" sonatas, when his music moved in a new direction toward a more personal, more intimate, sometimes even an introspective, realm of freedom and fantasy. In this period he had achieved a complete mastery of form, texture and tonality and was subverting the very conventions he had mastered to create works of remarkable profundity and beauty. It is also characteristic of these late works to incorporate contrapuntal techniques (e.g. canon and fugue) into the sonata form.
Beethoven himself described this sonata, composed in the town of Baden, just south of Vienna, during the summer of 1816, as "a series of impressions and reveries." The more intimate nature of the late sonatas probably has some connection with his deafness, which by this stage was almost total, isolating him from society so completely that his only means of communicating with friends and visitors was by means of a notebook.
For the first time Beethoven used the German term Hammerklavier to refer to the piano (although it was the next of his sonatas, Op. 106, that became widely known as the Hammerklavier sonata).
This was the only one of his 32 sonatas that Beethoven ever heard played publicly; this was in 1816, and the performer was a bank official and musical dilettante.
You might be interested in Andras Schiff's lecture on the sonata.