Castlewellan Forest Park and Castlewellan Lake are situated to the northwest of the village. The Arboretum in the park was begun in 1740 and contains plants and trees from many different countries including Spain, Mexico and Wales; the ‘Castlewellan Gold’ form of Leyland Cypress – originating from a single mutant tree in the arboretum and widely propagated from the 1970s – was selected by the park director, John Keown, being first named Cupressus macrocarpa Keownii, 1963. The Peace Maze was constructed in the park between 2000 and 2001. Until 2007 it was the longest permanent hedge maze in the world. In the very early hours of 7 April 2007 two youths died in a canoeing incident in the lake.
Castlewellan Castle, a Scottish baronial castle of 1856, overlooks the lake and the park.