Sitting between 67's Straight, No Chaser and 68's Monk's Blues, this is the last Monk recording his Quartet. 4 brand new compositions and hugely provocative sleeve artwork have helped this album retain its place as a milestone recording. 

Thelonious Monk once famously said "the piano ain't got no wrong notes", and this mantra is evident in his playing: full of angular, challenging harmonies combined with a harsh and percussive technique. Though his style of playing was unorthodox, he could also play runs and arpeggios with great speed and accuracy. All in all Monk would prove to be a long-lasting influence on jazz piano. Underground is the seventh studio album that Monk did for Columbia and features Larry Gales on bass, Ben Riley on drums and Charlie Rouse on tenor saxophone. A prolific composer, all but one of the tunes on this record are original compositions, all with different stories. Apart from the music, the cover is worth a special mention. It depicts Monk as a member of the French Resistance and is meant as an homage to Pannonica "Nica" de Koenigswarter. She was a member of the aristocratic Rothschild family and became a patron of leading jazz musicians, hosting jam sessions, driving them to gigs and sometimes even help out with paying the rent. In 1969 the cover won a Grammy for Best Recording Package