Option 1 - The Crystal Palace
The Arcology glitters like a diamond set in verdant rolling hills. Nature has reclaimed the land, and after many, many years there is very little sign of the near-disaster that led to humanity encapsulating itself in sealed biospheres.
Within the Arcology is a utopia of advanced technology and social harmony - but for some the deprivations needed to maintain the delicate balance that permits human survival chafe, and more importantly the controlling ideology is saccharine sweet in its effort to keep everyone on an even keel and incapable of discord. They yearn for struggle, for some sense that their existence has some meaning. They find the ideology that keeps their society running suffocating, and now they have a plan: a way to break out of their packed-in-cotton lives and strike out to create a new society of their own.
And soon, they will glimpse the iron fist that the placid, smiling faces of their rulers has hidden for generations.
Option 2 - The Lost City
The Great War ended everything.
Nuclear, chemical, biological and ultimately nanotech weapons tore down our cities and left the survivors trembling amid the rubble.
Slowly, and with great effort, tiny pockets of civilization have started to congeal amid the twisted wastes, but nothing is the same:
The Great War changed everything.
Radiation, retroviruses, DNA targeting nano-weapons, all these have combined to warp Nature into shapes we would barely recognise. Strange creatures have emerged from the ashes. Familiar creatures have changed, grown from our subjects to our rivals in the race to reclaim the Earth.
Against this backdrop, a light has risen:
One community of like-minded beings has slowly gathered the strength to build economic and intellectual wealth. A handful of perilous trade routes have been established between this center and a handful of areas that can feed into the civilization engine in various ways. Journeys can only be undertaken on an irregular schedule, but there seems to be promise: the Elders have found evidence among the scraps they have gathered of the knowledge of the Ancients that this is how the Ancients rose to such heights.
An expedition sets out, cutting its way through the glowing jungles and tribes of savages that sprawl across the landscape. But disaster strikes!
An attack, a storm, and the caravan is scattered.
Individuals, even small groups are doomed so far from the heart of the growing civilization - things are just too foul, too savage for the weak bodies of the parts of the whole.
A handful of survivors stumble on the entrance to ruins of the Ancients, and quickly secure themselves inside. As they rest with the winds of corruption howling outside, they soon realise that this is no ordinary ruin: this is just the entrance to a vast complex that not only stretches far and wide below the canopy of the jungle, but seems also to delve deep into the bedrock.
The world outside is still far too dangerous, but perhaps there are tools or valuable secrets surviving here that could be used to help them return to civilization alive.
But if random travelers can stumble on the entrance, so can many other things.
What horrors wait in the depths?
More importantly, even if the depths are still secure, will whatever still lives there be friendly?