Atmospheric ruins are all that's left of a once-grand castle built in 1221. Sitting at the north end of the village of Ferns, the castle is believed to have been the old fortress of Dermot MacMurrough. There's still a moat and walls, as well as a stone tower that offers excellent views from the top. If you do climb up, notice the hole at the top just to the left of the door. This was a "murder hole," through which defenders could pour hot oil or drop heavy stones onto invaders below. The castle was destroyed in the mid-17th century by parliamentarians led by Sir Charles Coote, who also ordered the deaths of almost all of the local residents.