Before the Apocalypse, Luna was a tourist area. An exotic resort destination for people from all the colony worlds. Three huge domes were vacationing spots for people wanting to enjoy the cultures of Ancient Egypt, King Arthur’s Camelot, and Chicago of the Roaring Twenties with several others nearing completion.

300 years later, characters begin their adventures on the moon.

On Luna, the old base was laid waste. However, the resort and most other installations were left mostly intact and the A.I.'s who maintain the facilities along with the guests and a few “new” life forms survive. The vacationers in the various theme park domes continue to live and thrive in the environments. As the vacations were total immersive experiences, little knowledge was passed down through the generations so most remain oblivious to the outside world and the nature of reality beyond the domes.

But some are becoming aware.... 

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Before the apocalypse, the Moon was a busy vacation stop. Tourists came to enjoy one of the three domes representing Earth’s past. People were gathered to a central location where they picked up the required chip for their dome of choice. They changed clothes to the proper historical garb and took a monorail to the dome for an enjoyable experience. Tourists usually became the royalty or upper society of the dome and enjoyed the best the period had to offer. They would stay a week or two and then trade in their brain chip and catch the shuttle back to Earth.

Characters begin their adventures on the moon after a deadly alien attack on the solar systems was stopped by unknown forces. Unknown to the characters, three hundred years ago vast alien armadas attacked all of the 77 worlds settled by mankind. The powerful defenses of mankind were blasted and each planet was destroyed from space. Special battle cruisers controlled by Artificial Intelligences retreated from all of those worlds and came back to lead a last defense of Earth. They came too late to the solar system and found Earth Prime in ruins.

After the apocalypse, the androids and artificial intelligences in the support warrens beneath the domes (sometimes called the underdome) repaired the damage caused by the aliens to the domes and the spaceport. Given the minimal resources of the Moon and the facility, these repairs took over 200 years to complete. During that time, the A.I.s also began a genetic improvement program among the humans who were now the domes’ permanent residents, using hypnotic techniques and brain chip manipulation to match men and women with the strongest traits. The result is that the humans now living in the domes are the most perfect specimens of humanity ever. They are smarter, stronger, taller, and faster than their ancestors. Along with selective breeding, the A.I.s stepped up the difficulty of quests in the domes, to hone the humans’ warrior instincts.
    
The reason for these measures is that the Moon installation was never meant to be self-sufficient. Its resources are limited. The A.I.s stretched every spare bolt, wire, and hyperbolic discontinuity assembler as far as possible, but a crisis point is near. Eventually, someone must make the trip to Earth Prime and bring badly needed repair parts and other resources back to Luna. The A.I.s and their androids are prohibited by programing from leaving the Moon. Having exchanged information with the S-ships before they withdrew to Jupiter, the A.I.s understand that humans will need every possible advantage to survive when they return to Earth Prime.