The Savage Land is an ecological preserve in the Antarctic ice shelf. It was set aside as a sort of zoo-- or biological research center-- by the Celestials who visited Earth some 100 million years ago.
The Savage Land is a deceptively complex facility that appears wild and overgrown, ringed by volcanoes and protected by an energetic field that preserves the temperature. At some point in the distant past, the Eternals briefly resided in the Savage Land, though their settlement was abandoned long before humanity rose up. The machine systems that maintain the Savage Land have gathered DNA samples from thousands of species over the millennia and stored them in complex biogenerative matrices underground. The Savage Land is a wholly self-contained enclave directed by a complex machine artificial intelligence. Given the power systems and the long term scope of the research plan, the AI can conduct multigenerational analysis of any given species to test for any number of parameters. Dinosaurs and prey animals share space with humans, lizards, and giant trees. The Eternals engineered an immortal man named Aurakles to serve as a multigenerational human component of the operation, instructing him to survey the external world periodically and examine humanity's effects on the global biome.
A few thousand years before Ragnarok, Atlanteans established a society in the Savage Land. The colony became something of a resort, named Atlantea. It was quite popular as a vacation spot. Relying more upon the complex technology of the preserve, the Atlanteans there did not face a natural disaster when Ragnarok struck them. However, without magics to sustain them, the community of refugees still rapidly collapsed due to fearful infighting. The bureaucrats occupied a northern block of residences dubbed Sylanda while a military coalition went southeast and occupied a mountainous area called Lemuria. The various Atlantean hybrid beast-men formed a third bloc, and the three groups bickered and fought for resources over the centuries. Within the space of a few generations, knowledge of ancient Atlantis was largely forgotten and all tribes regressed to a near stone-age level of sophistication.
It would be thousands of years before humans visited the Savage Land again. A Nazi troop transport, fleeing Allied pursuit, dove deep into a crack in the ice shelf and sailed hundreds of miles inland. The Nazi vessel beached, and the Allied forces chased them into the jungle. A handful of survivors endured the hostile land and joined forces with the local tribes in a bid for survival.
Later years would see more visitors to the strange Land, which generally seemed indifferent to this interesting new variable in the equation. It might have remained nothing more than a scientifically interesting locale save for the presence of the rarest of metals: Vibranium. This alone makes the Savage Land a conquest worth any price.