The circumgalactic medium (CGM) is crucial for galaxy formation and evolution, yet its properties are challenging to characterize observationally. In this talk, I will present an overview of an innovative technique using background gravitational arcs, termed "gravitational-arc tomography," developed by our "arctomo" collaboration over the past five years. Unlike traditional quasar absorption lines, which provide single probes of individual galaxy halos, gravitational-arc tomography offers multiple and contiguous extended probes of single galaxy halos. This approach allows us to disentangle degeneracies in signal interpretation, uniquely constraining the distribution, clumpiness, and kinematics of the diffuse CGM gas. Leveraging data from large telescopes across multiple facilities (HST, VLT, Magellan), our results reveal the complex structures and dynamic behaviors of the CGM. Recent observations highlight significant variations in gas clumpiness and motions, offering new insights into the interplay between galaxies and their surrounding environments. Looking ahead, I will discuss future prospects given the new and planned facilities.