The biggest part of the United Kingdom (also called the U.K.) is the island of Great Britain, which is made up of England, Wales, and Scotland. The U.K. also includes Northern Ireland, which is on another island. (South of Northern Ireland is the separate country of Ireland, which gained its independence from the U.K. in 1937.) Northern Ireland is just 12 miles from the island of Great Britain, across the North Channel of the Irish Sea.
Scotland and Wales are the most mountainous parts of the U.K. and are covered in knife-edged mountain ridges separated by deep valleys. This terrain was shaped some 20,000 years ago during the last Ice Age, when thick glaciers covered the land. When the Ice Age glaciers melted in northwest Scotland, they left behind thousands of lakes, called lochs. Long and narrow, some of the lochs are very deep. (Legends say that a giant monster called Nessie lives in Loch Ness in this region, also called the Scottish Highlands.)
The largest freshwater lake by surface area in the U.K., Lough Neagh (pronounced LOCK NEE), is in Northern Ireland. It stretches 20 miles long and nine miles wide. Rolling hills and plains dot the countryside of both Northern Ireland and England.