The Highland Boundary is a geological fault line that runs across Scotland, separating the Highlands from the Lowlands. It stretches for approximately 130 miles (210 km) from the North Sea in the east to the Atlantic Ocean in the west, passing through the Cairngorms National Park and the Grampian Mountains. The boundary is marked by a distinct change in landscape, with the Highlands to the north being characterized by rugged mountains, glens, and lochs, while the Lowlands to the south are generally flatter and more fertile. The Highland Boundary has played a significant role in shaping Scotland's history, culture, and economy, and remains an important geological and geographical feature of the country.