Subterranea is a kingdom beneath the surface of the Earth. At one time, it was the home of the Deviants. Subterranea consists of a seemingly planet-wide network of caverns lying miles beneath Earth's surface. However, since Subterranea also extends to Monster Isle^[3] and Monster Isle has tunnels linking it to the center of the Earth,^[4] therefore, consequently Subterranea is also connected to the center of the Earth.

Twenty thousand years ago, the priests and intellectuals of the city of Netheria in the southern part of the Atlantean continent foresaw that Atlantis would be attacked by the Deviant Empire, which was based in Lemuria; therefore, the people of Netheria enclosed their city in a dome of an unknown plastic-like substance and both excavated and fortified their city's foundations. Consequently, when Atlantis sank, Netheria remained intact and its people survived, having discovered a means of recycling their air supply. Netheria sank down even more deeply over the years until it finally came to rest in a huge sub-sea cavern. The Netherians renamed their realm the Netherworld, and are now known as the Netherworlders.

The Fantastic Four discovered the Mole Man and a race known as the Moloids dwelling in these underground tunnels. The monsters of Monster Isle also call this place home.

Tyrannus also made Subterranea his home, which inevitably created friction between him and the Mole Man. In Subterranea, Tyrannus came upon a stockpile of abandoned Deviant technology, which he used to attack the surface world. On one such attack, he discovered the Fountain of Youth and on another, he became the lover of the Netherworld's queen, Kala.

The Lava Men are a race from Subterranea made of living lava. They first came into contact with the surface world when their king, Basallo, sent their supreme warrior, Molto, to investigate whether the surface world would become a threat to Subterranea. There, Molto was manipulated by Loki into attacking Thor, but after he came to his senses, he returned to Subterranea and informed his king that the people of the surface world were peaceful and, therefore, not a threat to them.^[5]

Alternate Realities

House of M

In the House of M reality, Harvey Elder was the king of Subterranea. He was building it into a paradise below the ground for his beloved Moloids, until the Fearsome Four came and destroyed them all.

Earth-828

In this reality, Subterranea is an underground civilization as its name suggests, inhabited by Moloids and Deviant Mutates, that was known to the surface dwellers only in stories and led by the so-called human the Mole Man.^[6]

Earth-1610

In this reality, Subterranea is located "1.4 miles below the surface world". It is a "cave system connected by millions of tunnels across the world." Arthur Molekevic located his original subterranean headquarters below the Baxter Building to keep an eye on its occupants, in particular his unrequited love, Sue Storm. Molekevic had discovered advanced technology from an ancient underground race that helped him develop this underground world.^[7] Molekevic also created his Ani-Men, who faithfully served him. Lava Men also exist in this underground system as well.^[8]

• Abysmia - An underground country that was founded by some of the first Europeans to arrive in North America.
• The Forever City - An abandoned underground city that was once used by the High Evolutionary. It was raised to the surface world in the United States, with its inhabitants wanting their city to be declared its own independent nation.
• The Fountain of Youth - An underground fountain with magically-powered water which Tyrannus uses to keep himself young.
• Lechuguilla - One of the Moloids' cities.
• Lyonesse - An underground kingdom that was created by the Deviants of Armechadon beneath Manhattan.
• Meramec - An underground underwater city that is inhabited by aquatic Moloids.
• Netheria - A former city of Atlantis that predicted the continent's destruction and isolated itself from the rest of the world.
• The River Lethe - An underground river whose water causes amnesia to anyone who either drinks it or bathes in it.
• Sinister London - An underground city that is based on the surface world's city of London, England and was built by Mister Sinister in the Moloid caverns beneath Anchorage, Alaska.
• The Valley of Diamonds - An underground valley that is made up of so many enormous diamonds that their brightness blinds anyone that sees it or even looks at it. Anyone who wants to travel through it must wear special glasses in order to do so.

• The Deviants of Earth - in the past
• The Deviants of Armechadon
• The Deviant Mutates
• The Mole Man (Harvey Rupert Elder)
  • The Moloids
• Tyrannus (Romulus Augustulus)
  • The Tyrannoids
• The Ghouls
• The Gortokians - extinct
• The Lava Men
• The Lizard Men
• The Molans
• The Netherworlders