Some scientists are pushing for a sample return mission to Mars in which the robot wouldn't simply scoop up soil from the surface (though they want to do that, too) but instead have a rover enter a cave or lava tube and collect samples there. Since the surface of Mars is constantly exposed to radiation, they argue the best place to look for life-- past or present-- would be subsurface. Protected areas like caves or lava tubes, where rock blocks incoming radiation, might also work. Plus, they point out, such places could preserve a history of life on Mars, as they do on Earth.
Future life on Mars could also be served by such a mission, they point out. Lava tubes could be excellent sites for the first human settlements on Mars, as they would provide both protection from radiation and a consistent, controlled environment.
Of course, if Martian life already exists in such places, that could complicate or delay any human missions to the Red Planet.