The discovery of cosmic rays with energy exceeding the Greisen-Zatsepin-Kuz'min limit set by the cosmic background radiation has created an interesting and challenging problem for astrophysics. There are three basic questions associated with their existence: What are these rays? Where are these rays made? How did they survey the journey through space that is filled with CMB? Since the flux of these extremely high-energy cosmic rays (EHCR) is extremely low, to detect enough of these rays for study would require a detector of extraordinary size. OWL is designed with an aperture that is over two orders of magnitude larger than the combined aperture of the existing detectors. By its design, OWL will also be able to study the nature of EHCR and their arrival direction distribution. We will discuss the physics of the highest energy cosmic rays and the proposed detector.