On Earth-Two in the early 1940s, Superman built his original Fortress, which he referred to as his "Secret Sanctuary" or "Secret Citadel", at the top of a remote mountain-peak just outside of Metropolis.
He later constructed a second Fortress in the "polar wastes".
The Arctic Wastes
In May of 1949, the name "Fortress of Solitude" is employed for the first time in the chronicles and, also for the first time, Superman's sanctuary is depicted as being located in a region of ice and snow, described only as "the polar wastes." Superman explains, "I built it here in the polar wastes because the intense cold keeps away snoopers."