Pacifo

An ancient, sunken continent—located somewhere in the Pacific Ocean—whose sole surviving "remnant" is "a glass-enclosed city of ancient, weird design" which can be raised to the surface and then submerged like a submarine and which serves for a time as Lex Luthor's base of operations.

"You'll admit it was a miraculous achievement!" boasts Luthor. "Working underwater, I raised a glassolite-dome over the city, drained out the water, then raised the city to the surface of the ocean."

Pacifo is destroyed by Superman in Spring 1940 (S No. 4/2)