Bordered by the Derryveagh Mountains (Derryveagh means "forest of oak and birch"), Glenveagh National Park encompasses 24,000 acres of wilderness—mountain, moorland, lakes, and woods—that has been called the largest and most dramatic tract in the wildest part of Donegal. Within its borders, a thick carpet of russet-color heath and dense woodland rolls down the Derryveagh slopes into the broad open valley of the River Veagh (or Owenbeagh), which opens out into Glenveagh's spine: long and narrow, dark and clear Lough Beagh.
He died in 1885 without returning to Ireland, but his widow, Cornelia, moved back to make Glenveagh her home. She created four gardens, covering 27 acres; planted luxuriant rhododendrons; and began the job of making this turret-and-battlement-laden 19th-century folly livable. At the end of a dramatic 3-km-long (2-mile-long) entryway, perched over the lake waters, this is a true fairy-tale castle. Like a dollhouse Balmoral, its castellated, rectangular keep, battlemented ramparts, and a Round Tower enchantingly conjure up all the Victorian fantasies of a medieval redoubt.
The gardens and castle as they appear today are almost entirely an American invention, the product of the loving attentions of Glenveagh's last owners, including Kingsley Porter, a venerated professor of medieval art history at Harvard. He then passed the property over to U.S. millionaire Henry P. McIlhenny, who bought the estate in 1937 and, beginning in 1947, lived here for part of every year for almost 40 years. An avid art collector and philanthropist (his collection of Degas, Toulouse-Lautrec, and Ingres masterworks now resides at the Philadelphia Museum of Art), McIlhenny decorated every inch of the house himself in faux-baronial fashion and entertained lavishly.
Beyond the castle, footpaths lead into more remote sections of the park, including the Derrylahan Nature Trail, a 1½-km (1-mile) signposted trail where you may suddenly catch sight of a soaring golden eagle or chance upon a shy red deer. Take time to visit the 2½-acre Pleasure Grounds, a sunken garden at the heart of the estate with a sinuous lawn and Japanese maples.
A shuttle bus runs from the visitor center to the castle, and on weekends a bus service drops you off at the start of a 90-minute walking route. One of the highlights for hikers is the Lough Inshagh Path, a quiet stony dirt track which will take 2½ hours to walk one-way. Bike hire is also available from €6.