Mountains have steep sides and occur in ranges, with the highest being Mount Everest at 8,850m above sea level. They contain valleys between peaks and have small villages along narrow roads, while rivers flow through valleys. Key features include summits, slopes, and feet, and the Himalayas contain the highest 14 mountains. Glaciers form where rivers are permanently frozen, and mountains also exist undersea and provide about 80% of the world's fresh water.