The document discusses potential future human habitats in space. It describes how scientists are developing radiation-shielding bricks for building homes on Mars. However, living on Mars poses many challenges. The document also discusses physicist Stephen Hawking's view that in the future, humans may need to move to other planets or live in space cities to survive threats on Earth like nuclear disasters. It provides an illustration and description of a conceptual space house design within a larger space city. Key considerations for living in a space city include costs, life support systems, transportation, and social organization.