Amidst the bombast of Nirvana-influenced alternative rock in the '90s, a handful of Chicago-based musicians pioneered the genre of music tagged by critics as "post rock." Mixing a heady compound of jazz improvisation and outsider indie mentality, post rock provocateurs established quiet musicianship as the overarching aesthetic in the face of the loud rock dominating the mainstream. Among the post-rock explorers were five souls known as Tortoise. Throughout their 17-year career together, these Chicagoans have proved smart music can be pretty. In contrast to some '70s prog rockers, Tortoise isn't ashamed of its talent, nor is it pretentious. John McEntire (drums, keyboards), Doug McCombs (bass), John Herndon (drums, keyboard, vibraphone), Dan Bitney (percussion) and Jeff Parker (guitar) dabble in free jazz and ambient music wrapped in a rock mentality, gaining critical acclaim and being generally credited with saving alternative/indie music from itself. And they've created a cottage industry of post-rock outfits: The Sea and Cake (McEntire), Isotope 217 (Bitney, Herndon, Parker), Brokeback (McCombs) and the Chicago Underground Duo/Trio/Orchestra (Parker). After almost two decades of reshaping the boundaries of indie rock, one question remains: What comes after post rock?