'The Cage.'
It was the last known stronghold of humanity in The Cage—or at least, judging from the first season, it was. The ending contained a reversal, but up to now, there had been no clues at all.
The Lighthouse had once been an airborne prison. After being modified by several generations of people, it had eventually become an object resembling a gigantic flying mushroom.
The diameter of the 'mushroom' region was 608 meters (search for '[The Cage] I calculated how big the Lighthouse is' on Bilibili; the official response gave its diameter as 608 meters).
Its vertical length was approximately 800 meters, and it had a large number of suspended areas beneath the 'mushroom' region, enough to accommodate more than ten thousand residents.
Within this flying stronghold known as the Lighthouse, humanity was divided into two classes.
'Upper Class' people possessed superior genes, strong disease resistance, and robust physiques, giving them a higher survival rate in this world.
'Dust Persons' had comparatively inferior genes, but in reality, they were almost no different from the Upper Class. They were simply a group whose survival rate was lower than that of the Upper Class.
Of course, the most interesting setting in The Cage was the 'Dawn Hall.'
The Lighthouse's medical and research teams would select, from among all the Upper Class people, a man and a woman who were most suitable for giving birth to the next generation.
Then, the two Upper Class individuals would put on golden masks and, under the guidance of a group of believers known as the Light and Shadow Society, enter a room called the Dawn Hall.
After that came humanity's most instinctive act of reproduction, providing the Lighthouse with the highest-quality next generation.
There was a high probability that the two Upper Class people did