A fascinating quest for extraterrestrial microbial life in extreme environments is dealt with in the present chapter. Subsurface environments on extraterrestrial bodies tender shelter to microorganisms from aggressive exterior parameters. Microbial life is profuse and highly prolific in the subsurface of Earth. Caves are typical ecosystems where both microbial growth and secondary mineral precipitation are pronounced by steady physicochemical parameters. Lava tube caves are prevalent in volcanic territories on Earth, providing entrance to subsurface microbial environments and an abode to widespread microbial communities. Caves are also the sites for the development of exploration strategies and new technologies for subsequent voyages to Mars. Lava tubes and cave-like characteristics have also been spotted on Mars based on orbital imagery and remote sensing records. By resemblance with terrestrial caves, Martian caves might behold secondary mineralization that would enlighten us on aqueous activity long ago, apart from representing the ideal spots to look out for biosignatures.