The beautiful and dramatic mountain of Benwisken is a part of the Dartry Mountain range in the ancient kingdom of Carbury in north Sligo, bordering Co Leitrim. The peak of Benwisken blocks the entrance into the Gleniff valley, a huge glacier-formed hollow in the north side of the mountain range with the mysterious Diarmuid and Grainne’s cave in the cliffs to the rear of the valley. 

The native rock is a hard Dartry limestone, overlaying a core of sandstone. The distcintive peak of Benwisken was carved and sculpted by the passing glacier, resulting in an unusual mountain shaped like the forever-frozen crest of a mighty wave.

There are many ancient sites scattered about the base of the mountain: medieval cashels, stone walls, megalithic monuments, and the church founded at Keelogues by St. Molaise of Inishmurray and Devenish. The ancient medieval road leading from Glenade to Carney passes under Benwisken and Benbulben, through some of the most fairy-haunted territory in Co Sligo.

The mountain is covered with a mantle of blanket bog that holds water like a sponge. The top of the mountain is covered in sink holes and swallow holes, where water drained down into the stone, carving out the gallerys and tunnels behind Diarmuid and Grainne’s cave.