Glenarm Castle and Demense provides a central focus of interest and has been an ancestral home of the McDonnell clan for over 400 years and the family seat of the clan since 1750, before this it was at Dunluce Castle. The castle has a superb walled garden which is open to the general public during the summer months. The foundations of the present castle date back to 1636 and was built by Sir Randall McDonnell, the Earl of Antrim, it was rebuilt in the 1750s and again in 1825 when the Barbican, outer walls and Castle Street were constructed.

The castle was gutted by fire in 1929 and rebuilt in keeping with its character, a further fire in 1967 also required restoration of part of the castle. We know that the very first castle in Glenarm was let to the Bissett family during the 13th century, they came from Scotland to take up lands along the Antrim coast. In 1399 the marriage of Margery Bissett to John Mor McDonnell of Kintyre brought the beginning of what would become a shift of power to the McDonnells who would eventually control five castles along the north coast between here and Dunluce.