The remains of Guesdian Castle can be seen atop the hill while standing in Guesdian Graveyard. The opposite side of the castle ruin, which cannot be seen from the Trail, is in the shape of a great arch. The castle stands 20ft wide inside.
The castle is said to have originally been rectangular, but today, only the remains of the east and west walls are standing connected by the remains of the roof.
Guesdian castle was a Burke castle, and in 1574, it was occupied by Riocard an Iarainn, legendarily known as Iron Dick. He was the husband of the famous pirate queen, Grainne Uaille (Grace O Malley) and the father of Tiobóid na Long, who was shot by his own brother-in-law and is now buried in Ballintubber Abbey.