On the banks of the River Boyle is the finely preserved (and reputedly haunted) Boyle Abbey. Founded in 1161 by monks from Mellifont in County Louth, the abbey captures the transition from Romanesque to Gothic style, best seen in the nave, where a set of arches in each style face each other. A glass wall was added on the northern side in 2011 to prevent the arcade wall and buttresses holding up the roof from collapsing.
Unusually for a Cistercian building, figures and carved animals decorate the capitals to the west along with, more bafflingly, pagan sheila-na-gig fertility symbols. After the Dissolution of the Monasteries, the abbey was occupied by the military and became Boyle Castle; the stone chimney on the southern side of the abbey, which was once the refectory, dates from that period.