The Fortress of Solitude Overview
Situated deep within the arctic lies Superman's Fortress of Solitude, also known as the "Crystal Palace" due to its outward appearance. The Fortress has the appearance of a giant spiky crystal ball and is much larger on the inside than it appears on the outside.
The Fortress has unique properties that makes it perfectly suited for Superman's needs. Firstly, because of the unique Sunstone Crystals that serve as the Fortress' power source, it is completely invisible to satellite imagery -- only appearing to be another ice formation in in the Arctic unless you know exactly where to look and what to look for. Secondly, because of the Sunstone Crystals that comprise the Fortress, the Fortress is almost as durable as Superman himself making it incredibly hard to destroy except with the most drastic of means. Finally, the Fortress was used as a bastion of absolute Solitude for Superman. It is built specifically to block out all external sound and images from Superman's senses, allowing him a perfect place to be completely alone and exiled from the rest of the world.
Only few have actually seen the Fortress and even fewer have been inside thanks to the genetic key that is required to open it. As a result, only members of the House of El and their guests ever really get to enter the Fortress. To enter, one must pass through the large doors, that will phase them through and into the Fortress. Those not possessing the Kryptonian genome will find themselves teleported to Metropolis when they attempt to pass through the doors.
