About repression, goverment etc.
The current highlighted topic is "Very Large Floating Structures" (VLFS). Shortly floating city projects. Why it is hot topic, is because main amount of earth surface water-seas are international waters - meaning outside of countries jurisdiction. Every coastal country has 12 miles of radius border from its coastline - meaning its his territorial sea. And 200 miles for economic exclusive zone. Leaving enormous amount of water under internationally free.
What it means?
You can basically create artificial islands and start a new nation-country in international waters. There are quite a lot Sea-nation projects which try to create those islands with core principle that it would be self-sufficient and non-dependent from the continent. And they claim to create social-experiments, trying ti test new democracy ideas, country-repression free - aka utopias to be reality. These would be quite costly, but interesting projects and these are financed highly at moment.
Google-Youtube: Floating cities, Very Large Floating Structures, artificial floating islands, Seastanding Institute.
About the underground living.
I could not find the source i used to deal with, but terms like Earth House, Earth Sheltering has similar ideas. These houses are built mainly in deserts, hot places to create cool climate. They are also self-sufficient, solor powered etc. But thet do not go that deep into earth. Generally maximum 20 meters or so, but in commercial sense maybe 10 meters could be affordable. Previously Earth Housing was used to build use under hill like Hobbit :) to reduce cost for heating - it has quite dissapeared nowadays.
Underground living and sheltering is linked with severe weather, nature catastrophes and therefore mainly information is about those kind of shelters that offer it only for short period of time. Earth housing is meant to be lived in - decent rooms etc.
Tolerance Limits of People for Cold, Heat and humidity in underground sheltershttps://books.google.ee/books?id=-mErAAAAYAAJ&pg=PA31&lpg=PA31&dq=Limits+for+Cold,+Heat+and+Humidity+in+Underground+Shelters&source=bl&ots=a8WevBesLJ&sig=yMId677gb-4crIiwrcTNYGfxxJk&hl=et&sa=X&ei=NnWEVfnjDuqoygOXpaqYCA&ved=0CCsQ6AEwAg#v=onepage&q=Limits%20for%20Cold%2C%20Heat%20and%20Humidity%20in%20Underground%20Shelters&f=false