Learn about high-energy astrophysics and cosmic phenomena in this Pancharatnam lecture delivered by Professor Subir Sarkar at the Raman Research Institute. Explore the fascinating world of cosmic rays, their detection methods, and their impact on our understanding of the universe. Delve into gamma-ray astronomy, air shower physics, and the cosmic ray energy spectrum while examining the relationship with cosmic microwave background. Discover large-scale neutrino detectors worldwide, with special focus on the IceCube detector and its Deep Core component. Investigate various sources of cosmic rays, including galactic centers and exotic phenomena, while understanding the principles of multimessenger astronomy and real-time alert systems. Gain insights into low-energy cross sections, cascade events, and the future prospects of neutrino detection with IceCube Gen 2.