A huge limestone cave, it is the most famous in the area. Discovered in the early 1970s, this 1,300m (4,265-ft.) cave is pretty impressive. The name Gosu, which means "field of tall reeds," comes from the fact that the area used to be filled with fields of tall grasses. After the cave was discovered, rough stone instruments were excavated from the cave's entrance, showing that this used to be a home to prehistoric people. The average temperature inside the cave is 59°F (15°C) throughout the year. Many of the rock formations have names like Octopus Rock and Virgin Mary Rock. About 120 different stalactites and stalagmites are found here. Because the inner parts of the cave are colder and you sometimes have to hold metal railings, it is recommended that you wear gloves in the winter.