All the sanctuaries of Apollo in Greece and Anatolia were built at or near the springs because he is the god of prophecy. The sanctuaries of Apollo were sometimes built directly on next to or near spring water coming out of the cave, as in Smintheion. Caves, sacred places for people living in rural areas at the beginning for sheltering and communicating with the gods, lost their functions, albeit a little, with the birth of temples. According to ancient sources and coin descriptions, the cave in Smintheion is understood to have been an essential sanctuary since the establishment of the Apollo Smintheus cult. Construction of the Hellenistic temple near the cave where the water source comes out, the cult has lost its function, but the water coming out of the cave has always been used in the service of the gods. Although Apollo Smintheus (Apollo, the lord of mice) was initially known as a god associated with mice, it is known that mice actually aid in divination. However, in the inscriptions at the entrance of the Great Bath in Smintheion, it is understood that a priest, who contributed to the agonistic games in the 2nd century A.D., was expressed as a hypophet, carrying out a cult practice related to water. Ancient sources, inscriptions, and coin depictions reflect this deep-rooted tradition of the existence of this cave and spring in Troy, as Apollo is a god of Anatolian origin. Therefore, this cave and spring to the east of the Temple of Apollo Smintheus must have been used for divination. In the first part of this study, geographical features, topography, and geological structure, which were the reason for the water source in the establishment of Smintheion in this area, were discussed. Afterward, the ancient texts about the cult of Apollo Smintheus, the inscriptions, and archaeological findings obtained from the excavations were mentioned, and it was revealed that the cave where the water came out was used as a sacred cave, and the spring was used for divination.