Inside the ruins of the Roman bath complex at Ancient Salamis in north-eastern Cyprus. For a general description of Salamis see here.
Although Roman in nature, this bath complex was actually reconstructed by the Byzantines in the fourth century following earthquakes in 332 and 342 AD. These complexes comprised marble-lined pools, fountains, sweating room (sudatorium), cold (frigidaria) room and hot room (caldarium). This is a shot of the sudatorium or sweating room, and you an see the exposed underfloor heating known as a hypocaust (see my earlier post here for an explanation). I’m not 100% sure, but the pool in the previous post may have been the plunge pool of the caldarium.