The Fortress of Sanctuary was Samantha Arias's Kryptonian stronghold located in a desert location. It also serves as a repository for all the knowledge of the Kryptonians, including that of their now-destroyed homeworld of Krypton. After a fight between the Supergirl's team, The Legion, and the Worldkillers, the Fortress was destroyed and turned back into sand.
Samantha Arias took a crystal retrieved from her spaceship. It began glowing, and she followed its light out into the middle of the desert. She followed the beacon's signal to the middle of a clearing. All of a sudden, the ground shook and pikes made of rock emerged to form creating the Fortress of Sanctuary. Samantha went inside the structure and placed the beacon into a Kryptonian computer console panel that caused everything around her to activate. A holographic projection emerged, and told her she had answers for her questions. Sam asked as to where they were, and the projection told her that it was her Fortress of Sanctuary, a piece of her dead homeworld, Krypton.
Reign's version is a blackened cave, with crystal-like rocks protruding from the ground and a dark, cavernous interior. It is dark in color and pieces glow red in the darkness. The Fortress is planted outside somewhere in the desert and is held up by many huge desert-like columns. The crystalline structure of its buildings and crisscrossing crystal towers.
- When the Legion's cruiser located the Fortress of Sanctuary, it showed its location on a map of Kazakhstan, rather than the United States, as was previously assumed.