Nepal has the world's longest cave system, the Siddha Cave.

Nepal is home to the world's longest cave system, the Siddha Cave. Located in the Siddha village of Kaski district in western Nepal, the cave stretches for over 50 kilometers and is estimated to be around 10 million years old. The entrance to the cave is located at an altitude of 1,980 meters, and the cave system consists of multiple chambers and passages, some of which are up to 50 meters wide and 20 meters high.

The Siddha Cave is a popular destination for tourists and adventure seekers, who can explore up to 2.5 kilometers of the cave's passages, which include underground streams, waterfalls, and intricate rock formations such as stalactites and stalagmites. Some of these formations are estimated to be over 300,000 years old. The cave is open to visitors from September to May, with guided tours available for those interested in exploring the more remote areas of the cave system. The Siddha Cave is considered a must-see attraction for anyone traveling to Nepal, especially for those interested in adventure tourism and spelunking.