Verflecse
Verflecse (pronounced "VERR-flecks") is a planet that, like the other two in its nebula, is the same size as Earth. It was once uninhabited by sapient beings before humans from Earth found a single and one-way portal to the planet several millennia ago. Left with only the things they had brought with them, they had to create their civilization from scratch. What came from that endeavor is a world of technocracy and a societal pseudo-caste system after the advent of the Spidernet.
It took at least a millennium for humans to devise the technology to leave Verflecse and visit their moons, Ripley, Leeloo, and Tima. Slowly, they built several space colonies, and, after their success, plans were made to explore more of their nebula and outer space itself, particularly the other planets they could see from their telescopes.
Creating space colonies, however, brought back the flesh-eating microorganism that nearly wiped out human society and caused the reliance on cybernetics and drugs. Since then, all space-related plans and intentions have ceased. Prior to this, humans frequently visited the moons, and the remnants of the space colonies are still present but completely abandoned.
The majority of Verflecse's surface has been explored. There isn't much of the surface world that isn't known in some way or form. Caves have been mined until they're exhausted of their assets, and most have been destroyed and filled in for the sake of human habitation. Underground locations are the only unknown parts of the planet, mainly because the city has been built from the ground up with zero interest in underground matters.
However, while not "underground" in the traditional sense, the few parts of the city that have been built over the planet's ocean excavate natural resources from the water. The only natural resources that originate from the planet, in fact, are oceanic creatures and water.
Natural resources
Water
An expensive resource, water is excavated from the planet's ocean and purified into drinking water. There would be more, easily accessible natural drinking water from caves and waterfalls, however humans destroyed those resources millennia ago.
Seafood
Seafood is also an expensive resource, considered one of if not the greatest delicacy on the planet, especially crustaceans.
Antis
After humans arrived on Verflecse, and some hundred years after they created their architecture that mirrored that of Earth's, they noticed their reflections had come to life. After studying it, they came to the conclusion it was a result of living on the planet itself.
They named these "other selves" antis and, upon learning how dangerous they can be, removed all reflective surfaces and materials.
What they didn't know was that by doing this, they created vengeful beings that would take any opportunity to overtake their bodies when even the slightest slip-up was made.