Subterranea is an underground kingdom below the Earth’s surface containing a system of caverns and tunnels that are spread around the world. Multiple groups have called Subterranea home, which extends to Monster Isle and is linked to the center of the Earth. It was first seen in Marvel Mystery Comics #10 (August 1940) and was created by Paul Gustavson and Ray Gill.

Subterranea’s history traces back 20,000 years to when Netheria, a city in the southern part of the Atlantean continent, was facing an attack by the Deviant Empire. Netheria’s leaders fortified the city by building a dome over it and developed a system to recycle the air so that the people would survive. Netheria remained in one piece when Atlantis sank into the ocean, but over the years the city sank further below the earth’s surface.

The underground world is more than simple dirt and rock caves. There’s the Valley of Diamonds that is filled with huge diamonds so bright that they can blind a person (Mole Man was partially blinded by the diamonds). It has a fountain of youth, an underwater city, an abandoned city that the High Evolutionary had used, and a city based on London built by Mister Sinister, called Sinister London.

The inhabitants of Monster Isle took up residence in Subterranea, followed by Mole Man and the Moloids. The latter’s story began when Mole Man, then engineer Harvey Rupert Elder, found Monster Isle while exploring his theory of a hollow Earth. He fell through a cave and into Subterranea where he began exploring the many caverns and decided to stay their permanently. Renaming himself Mole Man, he became leader of the Moloids and used technology and creatures created by Deviants to fortify his new home and attack surface dwellers.

Tyrannus also moved into Subterranea, causing problems with Mole Man and his people. Like the Mole Man, he found Deviant technology and used it against people on the surface.

The Lava Men, a group who are completely made of lava, continued the trend of Subterraneans who considered the surface dwellers to be a threat. King Basallo sent a warrior named Molto aboveground to discern if they would harm the Lava Men and he determined that their people were safe belowground.