Explore the third lecture in a series on 3D gravity, Chern-Simons theory, and Wilson lines delivered by Alejandra Castro from the University of Amsterdam. Delve into non-perturbative aspects of three-dimensional gravity and its connection to Chern-Simons theory. Examine the role of Wilson lines in both theories, providing insights into locality and its limitations. Begin with a quick recap of previous lectures before diving into advanced concepts such as Ishibashi states, cross cap states, and inner products. Gain a deeper understanding of the fundamental mechanics behind holography and the potential of 3D gravity as a simplified model of quantum gravity. Follow along as complex equations and mathematical concepts are explained throughout this 1-hour 14-minute lecture, part of the Infosys-ICTS String Theory Lectures series hosted by the International Centre for Theoretical Sciences.