Computational advancements in the past couple decades have propelled the capabilities to design, model, and benchmark nuclear reactor systems. However, the lack of high-resolution two-phase flow data has hampered the development and validation of high-fidelity models for computational fluid dynamics (CFD) and subchannel codes, in particular pertaining to light water reactor (LWR) systems. The Michigan Adiabatic Rod Bundle Flow Experiment (MARBLE) is a modular assembly designed to simulate scaled PWR and BWR assemblies. It consists of an adiabatic 8x8 lattice mock-bundle built by the research group at the experimental and computational multiphase flow lab (ECMFL) located at the University of Michigan. The facility has been specifically designed and instrumented to establish a high spatial resolution experimental database of two-phase flows in reactor assembly geometries and investigate the effect of grid spacers and mixing vanes on void drift across subchannels. The present research discusses the various working parts associated with the MARBLE facility. Here, we explain the methods used to estimate the pressure drop across the bundle as well and the superficial gas velocity. A shakedown test is examined in order to demonstrate the operation of the MARBLE facility. Tomographic measurements are then performed with the High-Resolution Gamma-ray Tomography System (HRGTS) designed and built in-house; the detector system has been extensively characterized in previously published work and was shown to achieve a spatial resolution of 1.0 mm. In the present research we discuss tomographic measurements of two-phase flows performed at the MARBLE facility. The experiments include four targeted sets of gas superficial velocities of j_g = [0.025, 0.05, 0.25, 0.5] m/s, arranged for uniform gas injection as well as concentrated injection for the four central rods.