highest mountain massif in the British Isles, named after one of its peaks—Cairn Gorm, with an elevation of 4,084 feet (1,245 metres)—part of the Grampian Mountains in the Highlands of Scotland between the Spey and Dee river valleys. The mountains are divided among the Highland, Moray, and Aberdeenshire council areas, whose borders radiate from the massif. Ben Macdui, the highest mountain in the massif, with an elevation of 4,296 feet (1,309 metres), is the second highest mountain (after Ben Nevis) in the British Isles. A winter-sports industry in the Cairngorm Mountains, centred on the town of Aviemore, has developed and expanded rapidly since World War II. Recreational activities include skiing, ice and rock climbing, and pony trekking. The associated Cairngorms National Nature Reserve, with an area of 100 square miles (259 square km), was established in 1954 and has rare flora and fauna.