The room is rectangular in shape, oriented southeast–northwest (L101, L102; 3.0 × 4.5 m, height 2.1 m; Fig. 2). It was hewn into a layer of soft limestone located below a thick, hard layer of limestone (thickness 1 m). The room was discovered when the western part of its ceiling collapsed (Fig. 3); the ceiling remained intact on the eastern side of the room. A heavy fill of sand was found in the western part of the room (Fig. 4); in the eastern part, the sand fill was shallower, leaving a 1.2 m space below the ceiling (Fig. 5). Due to safety concerns, the excavation was restricted to the exposed, western part of the room. The sand in the upper levels of the room was removed mechanically, but the walls and floor of the room were exposed manually.
A stairway (width 1 m; Fig. 6) cut in the western wall of the room led into the room. Since the western wall was not fully exposed and the stairway was completely blocked with sand, the precise number of steps is unknown. The bedrock floor of the room, the southern part of which was largely charred (Fig. 7), carried a very thin layer of occupation debris, comprising pottery sherds, light ash and sand. The sherds included parts of a fine-ware cup from the Early Islamic period (eighth century CE; Fig. 8) and other ceramic sherds, such as Byzantine-period jar sherds and a fragment of a bag-shaped storage jar. Half of a grinding stone, belonging to an upper rotary grinder, was found in the stairway (Fig. 9).
The subterranean room may have belonged to a Byzantine-period farmstead. The function of the room is unclear; it may have been used as a wine cellar and as a storing room for agricultural produce. Subterranean rooms dating from the Late Byzantine period have been found in nearby Horbat Be’er Shema‘ (Erickson-Gini 2011; Erickson-Gini, Dolinka and Shilov 2015:219–221, Plan 3, Fig. 14) and in several places in and around Be’er Sheva‘ (D. Varga, person. comm.). The potsherds from the Early Islamic period found in the room suggest that its use continued during this period. Although the nearby Byzantine site and water system at Be’er Osnat have not been excavated, it is probable that they continued to be occupied in the Early Islamic period, like other sites in southern Israel.