Реферат: This chapter describes the Ordinskaya Cave in the Fore-Urals region, Russia, which is the largest underwater cave of sulfate rocks in the world. The explored length of the cave is about 4900 m. The regional distribution of karst features indicated that a large amount of recharge entered the lower passages during all stages of development. The groundwater in the cave is aggressive with respect to sulfate. Discharge of water with higher mineralization was documented during the spring floods. During summer low-flow periods, subaqueous springs discharge waters under artesian conditions with a lower solute content. In the cave, the degree of saturation of water increases from the bottom to the top in the spring season and is the reverse in the summer. Seasonal variations in the groundwater chemical composition reflect the contribution from the artesian system. The geological data indicate a strong relationship between the karst features and the regional fault network. The characteristic features of the Ordinskaya Cave make it a model object of artesian hypogene speleogenesis. Speleogenesis in the Formation of the Ordinskaya Cave, Fore-Urals, Russia.