Split off from the crystal gazebo, the crystal fortress developed airborne spores, able to fly in the wind using setae-like extensions of their otherwise crystal-like casing, and basically went off to land to be huge. It grows in sporadic “monuments” throughout Darwin, Glicker, and Barlowe, contributing to soil by eventually dying and decomposing. With little competition or strong currents in its way, it has reached a colossal size supported by the feature that got it its namesake—as it grows, periodically one of its root-branches will start growing as if it was at the top, essentially forming what looks like a smaller crystal gazebo growing off of it. This gives mature individuals a rough pyramid-like shape at an awe-inspiring scale, making it comparable to a castle or a fortress, hence its name. As the soil is still developing and it is quite large, it is rather infrequent in most of its range, as is typical of large flora in plains and savannas; however, it can grow in much thicker densities in the forests.
The crystal fortress is otherwise much like its ancestor. Its trunk is made of a bone-like material using minerals taken from its environment, its photosynthetic crystals have a chitinous shell, and it has stomata-like pores all over its trunk for respiring. It is a mixotroph, getting energy from both sunlight and detritus.