The Fortress of Solitude is where Superman always goes whenever he needs some "me time". Personally, I think he retreats there just to get away from Lois Lane. The Fortress of Solitude is, as its name suggests, a fortress located in the frozen wastelands of the North Pole. It is constructed of ice and crystalline structures and was built through automated Kryptonian technology. In addition to throw pillows and other general knickknacks, the Fortress of Solitude is decorated with mementos relating to Superman's Kryptonian heritage. Entrance into the Fortress may be gained through a variety of methods, based upon which media it is shown in. On Smallville, Clark Kent could get there by way of a spatial rift activated through the use of Kryptonian crystals or symbols, many of which were found inside the Kawatche Caves in Smallville, Kansas. In other sources, access may gained by way of a large yellow key, which is actually constructed from condensed star matter, so that only one with a Kryptonian's strength level could even hope to lift it.
Sometimes Superman goes to the Fortress to gain insight from a holographic representation of his deceased Kryptonian father, Jor-El. On Smallville, this was where Clark Kent finally donned his infamous red and blue union suit for the first time. Superman's pal, James Olsen, once took Superman's cousin, Kara Danvers, to the Fortress.