Altar is a collaboration album between Japanesesludge/doom band Boris and Americandrone doom duo Sunn O))), released on October 31, 2006 through Southern Lord Records. A limited two-CD edition was released on October 23rd via Southern Lord with a 28 minute bonus track with Sunn O))), Boris, and Dylan Carlson, titled "Her Lips Were Wet with Venom". Inoxia Records released their own two-CD version in 2006 which features a bonus track on the first disc, "The Sinking Belle (Black Sheep)," and also features "Her Lips Were Wet with Venom" on disc 2. The triple-vinyl edition by Southern Lord contains all of the songs from their two-CD edition, additional pictures, and liner notes by Kim Thayil. This 180 gram pressing is 2,000 sets: Opaque Blue, 2,000 sets: Opaque Green, 1,500 sets: Opaque Yellow, 1,500 sets: Brown, 1,000 sets: Black. The Daymare 3LP version was released March 23, 2007 and features a bonus track not found on any other version of this release: "The Sinking Belle (White Sheep)." In addition to major players Sunn O))) and Boris, Altar also boasts an extensive roster of guest musicians/collaborators such as Kim Thayil (Soundgarden), Joe Preston (Earth, Thrones, Melvins, High on Fire) and Jesse Sykes (Jesse Sykes and the Sweet Hereafter) as well as long time Sunn O))) collaborators TOS Niewenhuizen and Rex Ritter. On December 10, 2007, the bands collaborated at the Forum in London along with a number of the guests featured on Altar for a unique live performance.[1] A 3LP picture disc version of the album, limited to 500 copies, was sold exclusively at this show.[2]