- Cyclopean cities of coral buildings
- Cities of rust-proof metal powered by electricity-producing fish that pump electric pulses through water filled cables
- Organic cities of living technology made from selectively bred/genetically engineered organisms
Anyone else got any other ideas to squeeze in?
What sort of beings do you suppose would make these cities? How would react if they knew that a submarine of ours was approaching their city? What if they had telepathy?