Hawkwind

These space-metal pioneers released their second record in 1971, to high critical praise and surprising commercial success (a Top 20 album in the U.K. at the time). A 15-minute exploration of single-chord astral travel, "You Shouldn't Do That," opens the album and is one of the band's signature moments. There was plenty of musical exploration going on in 1971 but no bands were as single-mindedly dedicated to the groove as Hawkwind. Even today, Acid Mothers Temple have been trapped in this wormhole -- and the path Hawkwind mapped toward it -- since their inception.