The Surprising Ways Mars is Hostile to Life

I can imagine one possibility:  Tunnel underground, and build an enormous vacuum sealed cavern.  Then suspend habitation units from the walls, anchored by non conductive materials.   This would block most of the radiation. 

 From the surface, pipes can bring electricity from solar and nuclear power cells.  Sterling engines might actually harness nuclear the best, due to Mars low temperature.  When the surface temperature is too high for the sterling engines to work, above 50 degrees Fahrenheit, the crew can go up to the surface for maintenance and exploration, and use battery heat pumps to keep their habitation pods warm, pumping fluid antifreeze from the heat Pumps on the habitation pods to surface radiators for direct heat exchange. 

Right now SHEDDING radiation seems to be the best place for researching habitability on Mars.   The surface radiation and radiation from nuclear power cells will need to shed most of itself to be acceptable for human living.   

There are a number of plant, bacterial, algal, fungal and proozoic species that consume radiation.   We need to study cultivation methods for these, and see which ones could survive in artificial habitats on Mars.   If Mars truly does turn out to be sterile, perhaps we can seed its caves microbes that will start to slowly build back up a thicker atmosphere.  That would take a few hundred thousand years, but something our descendants might benefit from