You come across a city in your travels in the strange world. The entirety of it - down to the tallest dwellings - are covered in a futuristic dome sheltering it from the elements. You're about to wonder if something survived out here when you see them. They're affixing what looks like a clear hazmat suit to their body as they step out of the dome, and they've parked something like a motorcycle, with a hover mechanism meant for traversing sand beside them.
Cautiously, you approach.
The Alien says: More travelers from who knows where? It's been a long time. Welcome to Isiliv, you're at one of the remaining domed cities of the Couloir. I have to admit, I have some questions. Would you mind following me for a bit? The radiation doesn't make its way past the dome, you'll be safe.
As you follow them inside, you learn more. The Desolated World is called the Couloir, and it is mostly desert aside from the massive stretch of forest nearly on the other side of the world from here, stretching up and down most of the latitude of the planet. The alien you're following is a Couler, the species named for the planet. While they were always hardy, the radiation on the planet killed off many of them before they could adapt.
They don't know about the Chasm. They just know there are rifts in the sky that a traveler will rarely fall through, sick with radiation and afraid, and if they're lucky, they'll get to a city in time. They're surprised you came equipped with gear to protect yourself. You're not sure how much to explain yet - you ask them to go first before you do. How did the world get like this?
You sit down in a boxy glass home, thick drapes half-covering the windows. Appliances light up around you, and the Couler sits across from you on a cooling mat strapped to a metal hexagon - a cooling seat? Before you can take in the technology further, the explanation begins.
The Couler says: The radiation mutated our fauna in the prism forest, making them massive and vicious. No one lives there anymore - cautious journies are taken, but nothing permanent. Homes built there are always destroyed by those monsters. The cities in the desert dwindled as their residents walked out into the sand never to be seen again, or died in their homes after a rare - but extant - failure in the domes. Most of the animals across the world died off because you... you were gone. They couldn't survive without a third sun, the few that could often became strange before dying off themselves. It's mostly little creatures and walking flora now.
The Eye says: I SEE. I CANNOT SAY IT IS WORSE THAN I EXPECTED, AS I NEVER SAW THE CITIES FROM MY RIFTS. I ASSUMED YOU HAD ALL DIED OUT, I RARELY SAW LIFE ON THE PLANET TO BEGIN WITH. THEN THE GIGAFAUNA CAME, BREAKING ME FREE FROM THE TUNNEL.
The Couler says: The monsters? They escaped?
The Eye says: I CANNOT HOLD THEM BACK. THEY ARE TOO POWERFUL EVEN FOR MYSELF.
The Couler says: What can I do to stop them? I hate the idea of our problem becoming an invasive species somewhere else.
The Eye says: PERHAPS YOU COULD FIGHT THEM BACK FROM THE RIFTS? KEEP THEM AWAY BEFORE THEY EVER COME TO OTHER WORLDS. I CAN SEND MORE TEAMS OF TRAVELERS HERE TO ASSIST YOU.
The Couler says: Please make sure that they're properly suited up. I'd hate to be the reason there's another casualty here.
The Eye says: OF COURSE. NOW I MUST RETURN YOU TO THE WORLD FROM WHICH YOU CAME. I WILL BE WATCHING.
The Couler says: I'll miss you.
what did you just miss