Piano Sonata No. 14 in C-Sharp Minor, Op. 27: No. 2, aka "Moonlight Sonata" (Ludwig van Beethoven)

I wouldn't consider myself a classical music aficionado by any means.  I'd probably fail miserably playing "name that tune" if you played me 10 different songs by different classical composers, back to back.  To be brutally honest, I think a lot of classical music is overblown, vanilla background music that's only suitable for doctors' offices or snobby shopping centers.
Nevertheless, I like what I like: compositions tinged with passion (either romantic or spiritual), interesting interplay among instruments and/or parts, and a strong rhythmic feel.
That's probably why I like Beethoven.
My favorite song of Ludwig's is what is commonly known as "Moonlight Sonata."  Beethoven himself never referred to it as such.  It was "Piano Sonata No. 14 in C-Sharp Minor, Op. 27: No. 2, Movement 1" to him.  It only was after Beethoven's death that German music critic and poet Ludwig Rellstab likened the composition to watching the moon shining down on Switzerland's Lake Lucerne.  Hence "Moonlight Sonata."
In actuality, it's more of an aching expression of love from Beethoven to his piano student, Austrian countess Julie Guicciardi, than an ode to the moon.  
According to the site Classic FM, sometime around 1797, Beethoven became quite ill with typhus--a bacterial infection spread by lice, fleas, and other vermin.  (Ahhh, the 18th Century...)  It's believed that this illness is what caused Beethoven to gradually lose his hearing.
Even before the illness and hearing loss, the poor guy had a tough time of it.  He finally got to meet Mozart in 1787 and was poised become his student, but he suddenly had to return home to Bonn, Germany, because his mother was dying of tuberculosis (or "consumption" in 1700s parlance).  Then Mozart died before Beethoven could return to see him.  Furthermore, Beethoven's father was a raging alcoholic, who spiraled out of control after the death of his wife, leaving Ludwig to look after his younger brothers.
So when he met Guicciardi in 1801 and fell for her, it provided a respite from the preceding years of strife.  
But in true romantic fashion, the story wasn't over there.
He eventually realized that nothing could come of the relationship because she was of a higher social strata, and she went on to marry someone else. 
So "Moonlight Sonata" is the sound of a tortured soul, deeply in love, realizing that it just can't be.  It's delicate yet profoundly powerful, and deceptively more complex and inventive than its arpeggios and rumbling left hand chords might betray.
Just absorb those chord changes through your headphones and have your Kleenex at the ready.