The Oylat Caves and Avcılar Caves in Türkiye's Bursa and Balıkesir showcase the most beautiful examples of underground geological formations in the southern Marmara region with their stalactites and stalagmites.

Oylat Cave, located in Bursa's Inegöl district, also famed for its meatballs, consists of two interconnected floors formed over approximately 3 million years along fault lines.

Hanging on the canyon slope, the 720-meter-long (2,362-foot-long) cave, with its horizontal orientation and completed fossil formation particularly captivates with its 7-to-8-meter-long stalactites and stalagmites.

Hosting nearly 300,000 visitors annually, the cave, which generally has a meandering profile, has narrow galleries from its entrance to the large collapse hall.

Alper Taban, the mayor of Inegöl, speaking to Anadolu Agency (AA) noted that the cave is situated in the area where Oylat Thermal Springs and Oylat Waterfall are also located and contributes significantly to the region's tourism.

Stating that the cave, with a height of 93 meters, maintains a temperature of 18 degrees Celsius (64.4 degrees Fahrenheit) year-round, Taban continued on to say that according to a rumor, it is said that the cave is much longer and could extend to Bursa.

"It was discovered with the works carried out by the governor of that period. We especially want visitors to the region to see this place. It's like a treasure hidden in a forest at an altitude of about 750 meters above sea level. Our Oylat Cave has an increasing visitor traffic every year. We believe that our observation terrace project in the area where the entrance of the cave is located will add value to the region," he explained.

Sıtkı Milli, the manager of Oylat Cave, on the other hand, mentioned that the cave, which has 85% humidity, is frequently visited by asthma and bronchitis patients.

Emphasizing his profession as a decorator, Milli said: "I have never seen such formations; there are layered water pools that have formed spontaneously. We have a route consisting of stairs made of galvanized sheets inside. It is a wonderful place formed by limestone over millions of years."

A 12-year-old boy, Mehmet Efe Şentürk, who visited the cave with his family, expressed that he had researched before coming here.

Şentürk, who noted that he was most fascinated by stalactites and stalagmites, said, "It takes 16 years for 1 centimeter of these formations to occur. It was very surprising to me. There are usually 500 steps in total, both up and down, making a total of a thousand steps. It is 1.5 kilometers (nearly 1 mile), but it didn't tire me much. To be honest, it was easy."

Avcılar Cave, formed from limestone in the Kızılçukur region of the Edremit district in Balıkesir, was discovered in 2012 when Mehmet Altay, a resident of the region, reported it to professor Abdullah Soykan, a faculty member of the Geography Department at Balıkesir University.

Accessible to professional teams from the important tourism destination Altınoluk in the northern Aegean, the cave is 22.5 meters deep and 145 meters long, containing stalactites, stalagmites and dripstone columns.

Soykan, stating that they realized during their study 11 years ago that the cave developed vertically, said that Avcılar Cave is a half-vertical, half-horizontal cave and has transformed into a fossil cave that has lost its activity in the so-called "vadose zone" (unsaturated zone) as the cave adapted to the rising mountains.

"As the mountains rose, the cave remained high, but it consists of three sections, first vertically, then horizontally and then vertically again. In fact, if the limestone in the area was wider, a much larger cave could have been formed here," he explained.

Emphasizing the importance of the cave's location, Soykan explained that the Edremit-Altınoluk corridor, facing south in the Kaz Mountains, is one of Türkiye's most important tourism destinations.

Indicating that Avcılar is the only cave in the region with tourism potential, Soykan said: "It needs to be turned into a tourism spot with landscaping. It is a very special cave with beautiful stalactites, stalagmites, dripstone columns, wall dripstones inside."

"Gas measurements of this place have also been taken. Harmful gases such as hydrogen sulfide, methane and carbon monoxide are at normal levels. Only the humidity is a bit high compared to the outside," Soykan added.

He concluded by saying that the temperature inside the cave is between 13 and 14 degrees Celsius year-round.