Hawkwind's second album was the one that solidified their position as underground heroes of the U.K. music scene; it's a milestone of post–Aquarian Age psychedelia and a sacred text of the space-rock genre it helped to inspire. Subsequent albums would venture into more overtly song-oriented territory, but here the standouts are trippy, jam-oriented riff-fests like "You Know You're Only Dreaming" and the 15-minute "You Shouldn't Do That," where Del Dettmar and Dik Mik's electronics and Nik Turner's heavily processed flute and sax smear spacy textures atop almost monomaniacally minimalistic figures. The interstellar excursions are set in relief by a few more conventional, downright folk-rocky cuts: the acoustic-based "Children of the Sun" and "We Took the Wrong Step Years Ago." But it was "Master of the Universe" that would become the band's signature song, setting its sci-fi lyrics against gritty hard rock riffs that would both help define space rock and influence the first wave of U.K. heavy metal.