Biodefense Chamber A is a room located on the Celestial Archives, Alinos, the Vesper Defense Outpost, and Arcterra. The chamber is always the ultimate room of every first Stronghold Void on all four of the worlds, and is the location of all Cretaphids. Biodefense Chamber A is intricately designed in the typical Alimbic style, with numerous patterns of circles and spirals on the walls and shades of pink and light purple. Destroying the Cretaphid within causes the Octolith, and numerous Energy Capsules to appear.