A number of critics and many classical music aficionados consider Schubert's String Quintet, Op. 163, D. 956, also known as his Cello Quintet, to be the greatest piece of chamber music ever written. It's certainly among the greatest IMO.
Also, if a solo piano work is considered to be within the category that is being asked about, I would suggest Chopin's Piano Sonata No. 3, Op. 58.
Regards,
-- Al
Also, if a solo piano work is considered to be within the category that is being asked about, I would suggest Chopin's Piano Sonata No. 3, Op. 58.
Regards,
-- Al