Underground was recorded in 1967, about 20 years into the career of this wholly distinctive and unorthodox pianist-composer. Whenever the understated saxophone talents of Charlie Rouse accompany Thelonious Monk, one is assured of an invigorating set of music--and this collection is no exception. Supported by Larry Gales on bass and the inimitable Ben Riley on drums, Monk and Rouse elaborate on immortal compositions like "Ugly Beauty." On "In Walked Bud," the quartet is joined by vocalist Jon Hendricks. With jagged themes and unusual variations of meter and key, Underground showcases an aging Monk's still-brilliant eccentricity on the piano. A good bit looser than much of Monk's earlier work, he and Rouse infuse this date with their tag-team humor and unrelenting musical enthusiasm. --Mitch Myers