Over the last decade I've been studying ultra-high energy cosmic rays, the most energetic and rarest of particles in the Universe. When these particles strike the Earth's atmosphere, they produce extensive air showers made of billions of secondary particles. While much progress has been made in nearly a century of research in understanding cosmic rays with low to moderate energies, those with extremely high energies remain mysterious. Detecting these particles is challenging because the highest energy cosmic rays are extremely rare. The especially interesting cosmic rays, with energies over 1e20 electron volts (equivalent to the kinetic energy of a tennis ball traveling at 85 km per hour, but packed into a single proton!), arrive on Earth at a rate of one per square kilometer per century! To record a large number of these remarkable events, the Pierre Auger Collaboration, with nearly 500 physicists from more than 90 institutions in 20 countries, built the largest cosmic ray detector. The Pierre Auger Observatory in western Argentina (the region where all the good Malbecs come from...) has a detection area ten times the size of Paris, or a bit larger than Luxembourg. In this talk I will explain the motivation to study ultra-high energy cosmic rays, I will describe the different detection techniques and the Pierre Auger Observatory. Finally, I will also comment on what's next in high energy particle astrophysics.