St Mullin's derives its name from Saint Moling who founded the monastery in the early part of the 7th Century. The original monastery was destroyed by Vikings in 951AD, and again in 1138AD. The surviving buildings are those of the mediaeval abbey built on the site in the 15th Century, incorporating some of the remains of the earlier church.

Today, the remains of the monastery are situated behind an extensive graveyard, and a 19th Century church, which now serves as a heritage centre. Notable amongst the ruins are a 9th Century cross depicting the crucifixion, the base of an 11th Century round tower, the surviving shells of various domestic and ecclesiastical buildings, and the abbey church. A Norman motte lies just across the road from the entrance to the site.

Despite its rich history, the ruins of the monastery aren't particularly impressive. Having said that, this is a fascinating site with some unique points of interest. It also benefits from being situated near St. Moling's holy well, and lying just above the River Barrow - which is well worth walking down to for its picturesque setting.