Do you have some list of the places in the ATOM universe we can use as a reference?
Generiton, Montana - a small town in Montana, USA of no great significance except for its close proximitiy to…
The Hollow Mountain - a mountain whose interior is actually an entire jungle-like ecosystem - specifially a kaiju-sized jungle. Tyrantis and Ahuul were the only kaiju inhabitants of this particular ecosystem at the time of their discovery. The opening to the Hollow Mountain ecosystem was sealed off shortly after.
The Nevada Nuclear Testing Site (Yucca Flat) - a real life location where the USA conducted several nuclear bomb tests. In ATOM, the tests conducted here hit upon a large vein of Yamaneon, causing a chain reaction that ripples throughout the entire underground Yamaneon system and forces several of the subterranean kaiju ecosystems up to the surface.
The Underground Valley - a kaiju ecosystem that is exposed to the surface via a large crack in the San Andreas fault line caused by the chain reaction mentioned above. This one had a shit load of kaiju in it.
The Serpent Temple - located in some small beach community in California that I have yet to name (it’ll probably be as silly/punny as Generiton though), this ancient temple has strange features unlike any other known archaeological site in the Americas. It was built by lizard people as a shrine/home for Gorgolisk.
The Jungle of Green Hell - located somewhere in the South American Jungle, this particular patch of land is owned by the eccentric and dangerous Professor Panic, a man set on disrupting the world order for personal gain. He experiments with ways to control kaiju using the soma berry plant.
Typhon Island - an immense island that emerged literally out of nowhere in the Pacific during the catastrophic Yamaneon chain reaction described above. Typhon Island is just lousy with kaiju, and gets more so as the story goes on. It’s also basically a kaiju paradise - plenty of massive trees, freshwater lakes, mountains to climb, etc. A perfect island for monsters.
Literally All of Japan - Japan has more kaiju in its country than the USA does, despite having much smaller landmass.
The Glaciar Oasis - discovered in the icy North of Russia, this massive Yamaneon-rich ecosystem was hidden by massive walls of ice until an unfortunate nuclear test broke down one of its walls. It was filled with ice age kaiju like Mastemuth.
The Tunguska Crater - A massive crater caused by a mysterious explosion near the Tunguska river, this giant hole in the surface of the earth exposed another subterranean kaiju ecosystem.
The Siberian Monster Zone - a large, uninhabited portion of the Siberian wilderness where most of the kaiju of Russia have been herded into and walled off. Keeping the monsters in there is hard, which is why the Russian government finally tried the one thing everyone was scared to do and used a nuclear weapon on a large crowd of the creatures. The result was unfortunate and the experiment was never repeated on the remaining kaiju in the zone.
Area 51 - a mysterious base in the middle of Nevada that conducts all sorts of strange as fuck experiments with things man was not meant to know. Has a small collection of captured kaiju to experiment on and use as guards.
Mars - the red planet of war. Mars’s ecosystem was utterly devastated by the civilized, sapient race of Martians, with its bidiversity at a preposterous low. Then it experienced its own age of monsters, with dozens of prehistoric kaiju coming out of the woodwork to lay the Martian civilization low. The surviving Martians learned to live with the kaiju and even worshipped them to some extent as gods, only to be attacked by the Beyonder Alliance. The combined strength of the Martians and their kaiju allies drove off the B.A., but at a cost that left their planet uninhabitable. The Martins quickly colonized Venus instead, bringing their kaiju with them.
Venus - a mostly inhospitable planet that produces strangely resilient kaiju like Karamtor. The Martians have bubbled colonies that siphon some of the unused resources of the planet while keeping the local weather and fauna at bay. It’s an uneasy but not necessarily antagonistic relationship.
The Beyonder Homeworld - by this point it probably looks like Coruscant from the Star Wars movies. It’s the center of an intergalactic empire after all. Most of the kaiju from this homeworld have experienced a lot of genetic tampering and could look like anything.
The Flewud Homeworld - a dark planet with short days and long nights, home of Mothmanud’s creators.
The Scalim Homeworld - a planet covered in utterly massive - i.e. mountain sized - trees. Almost all life there is aboreal.
The Feengup Homeworld - it’s a planet, but I haven’t thought particularly hard about it’s geography.
The Kwadsim Homeworld - like the Feengup Homeworld, I haven’t though particularly hard about its geography. Most of its species have quadrilateral symmetry though.
Zillser’s Homeworld - not sure what it’s like at all, but it probably had at least one really big swamp.
Feel free to make your own too!