Though it's not necessarily a bad quality, post-rock (especially as it trends to the more ambient side of things), can be an awfully passive listening experience, sweeping the listeners up in drifting buildup and inevitable crescendos without ever really confronting them. Challenging this paradigm, Sigur Rós get sonically adventurous with their seventh album, Kveikur, which finds the Icelandic three-piece delivering a darker and more aggressive sound on one of their most daring albums to date. From the opening moments of "Brennisteinn," the album's opening track that thrums to life through a layer of crackling static with a guttural, churning bassline, it's clear that the band aren't looking for gentle complacency from the listener. While the album might not be aggressive in the traditional sense, with big loud guitars and howling vocals, there's an eerie tension that runs throughout the album that counteracts the soothing flow of Jonsi's drifting falsetto, making the songs feel like a good dream that's always on the verge of going bad. While Kveikur isn't a complete reinvention of their sound, it's the kind of palette shift that shows just how versatile and creative Sigur Rós can be. Few bands can subvert the expectations of the listener quite like this, and even fewer can do it after seven albums. Kveikur isn't the kind of post-rock album that you throw on to listen to as you contemplate the changing of the leaves, but rather an album that explores the differences between the comforts of the day and the anxieties of the night, blending the bright and the brooding to create something bold and beautiful.