In recent times, there has been a significant increase in intermittent renewable electricity capacity additions to the generation mix. This, coupled with an aging electrical grid that is poorly equipped to handle the ensuing mismatch between generation and use, has created a strong need for flexible, advanced bulk energy storage technologies. In this paper, one such technology recently invented and demonstrated at Oak Ridge National Laboratory is introduced and characterized. Similar to compressed-air energy storage, the Ground-Level Integrated Diverse Energy Storage (GLIDES) technology is based on gas compression/expansion, however, liquid-piston compression and expansion are utilized. In common with pumped-storage hydroelectricity, hydraulic turbomachines (pump/turbine) are utilized for energy storage and recovery, however, pressure vessels are utilized to create artificial elevation (head) difference, allowing pressure head of several thousands of feet to be reached. This paper reports on the experimental performance of the first GLIDES proof-of-concept prototype, and presents formulation and results from a validated physics-based simulation model.