The Mourne Mountains are the highest range in Northern Ireland and one of its best-kept secrets. Walk the large sweeping downs and follow hiking trails across the high peaks, which are also favorites of mountain bikers and rock climbers, and you’ll understand why the landscape is said to have been C.S. Lewis’s inspiration for Narnia. Slieve Donard is the tallest peak at 2,780 feet, and climbers will be rewarded with views of Murlough Bay and Newcastle beach—and even across the Irish Sea to Scotland. A gentle hike up Ben Crom leads to a lookout over the Silent Valley and Ben Crom Reservoir. The impressive 22-mile Mourne Wall, which was built out of stone by the city of Belfast to keep sheep and cattle out of the local reservoir’s watershed, took 18 years to complete and crosses 15 mountain summits.