Radioactive World — Whether due to a legacy of atomic warfare unhindered by nuke snuffers or a simple profusion of radioactive elements, this world glows in the dark. Even heavy vacc suits can filter only so much of the radiation, and most natives suffer a wide variety of cancers, mutations and other illnesses without the protection of advanced medical treatments.
Seagoing Cities — Either the world is entirely water or else the land is simply too dangerous for most humans. Human settlement on this world consists of a number of floating cities that follow the currents and the fish. These city-ships might have been purpose-built for their task, or they could be jury-rigged conglomerations of ships and structures thrown together when the need for seagoing life become apparent to the locals.