Fortress of Solitude
The concept and name "Fortress of Solitude" first appeared in the Doc Savage pulps in the 1930s and 1940s. Doc Savage built his Fortress of Solitude in the Arctic and retreated to it alone in order to make new scientific or medical breakthroughs, and to store dangerous technology and other secrets. The Golden Age Superman did not have an arctic fortress, but instead a "mountain sanctuary" which was located in a mountain range on the outskirts of Metropolis. Here, Superman kept a diary, oversized tools for various projects, and other equipment and trophies.