I choose the second idea seed. So my civilization is in a paradise that is in a very tropical jungle. The main city it self is located with in a lake with many caves and tunnels connected to it so it can maintain a network with the other cities in the area. It is not the safest to travel through the jungle since of the harsh environment and the wildlife surrounding. But what gives them the advantage from the conditions that they most live in is this mineral that is like an magnet but instead of pulling it repels. They are a primitive culture but as engineered some creative ways to use the mineral/crystal to survive. How ever the they have been noticing that the crystal has been loosing some of its force and b/c of this some of the technology is failing or just not able to maintain certain survival mechanisms. They need to figure out how to be more efficient or need to venture out of the paradise to find more minerals.
Sketches and Ideas