Kızılelma Cave, which is one of the longest caves in Turkey, is located in Kızılelma district in Ayiçi village in Gelik region of Zonguldak province. Developing in the form of a sinkhole, the cave collects the waters of Ayiçi Dere and Aydın Creek.

The fossil of 30 × 10 meters is entered into the cave through the mouth and the water is encountered after 100 meters. With a total length of 10 kilometers of the underground system (Kızılelma-Cumayani), the cave is the second longest cave system in Turkey.