From the Round Tower can be seen on the summit of the hill the beautiful Gothic ruins of  St. Mary's  Abbey, an Augustinian foundation dating from the twelfth century.

St. Mary's was the Parish Church until 1603 and its tower still stands, roofless but otherwise intact. Set to the wall of the tower are several sculptured stones. One is a sculptured Celtic cross with human heads and spiral patterns.

In 1804 the beautiful east window of the Abbey was removed to nearby Monea Church on the mainland and is still there.

In the cemetery adjacent to St. Mary's Abbey stands a sculptured High Cross, carved on the east face of the shaft with a representation of the Crucifixion. Other carvings are of ornamental patterns, and of a human head. There is also a niche for a relic.