In this paper the main scientific activities, over 20 years, of our group at Mt. Blanc Laboratory are described on the basis of three experiments: SCE (Spark Chamber Experiment), NUSEX (Nucleon Stability Experiment) and LSD (Liquid Scintillation Detector). A first noteworthy step to the muon physics deep underground has been done by SCE in the 70's, while at the present time a very important impact is given by NUSEX and LSD experiments, now fully running, playing a heavy role both on the elementary particle and astrophysics research. The results of these experiments are discussed focusing expecially on the physics of muons of atmospheric origin and of those locally originated at Mt. Blanc Laboratory, 5000 m w.e. deep underground.