Tlos has two bath structures. One of them is called Great Bath because of its large dimension. This bath is located on a slope near the southwestern part of the city center. It consisting of three adjoining rooms linked to each other through doors, follows the plan scheme of the typical Lycian baths. The eastern room of the bath with a monumental gate is the cold room (frigidarium). The apsidal end of this room with seven arched windows has a picturesque view of the valley. A small pool accessed through steps was also built in the apsidal part of the cold room. Two door openings placed within the western wall of the cold room provide access to the warm room (tepidarium). Different from the cold room, the warm room was heated from the floor and the side walls through the use of a heating system. Because of a small Byzantine church built into it, the warm room lost most of it original features. The cold room in the Byzantine period was also used as a cemetery by the inhabitants. The western room of the Great Bath was used as the hot room (caldarium). The heating system of the warm room was also used in the hot room. The changes made in the bath in the Byzantine period also included the hot room: it was transformed into the narthex of the church. Although it was first constructed in the Early Roman period, the Great Bath saw renovations in the second and third centuries A.D. The bath was converted into a church in the eleventh century.