Bonamargy Friary stands off the Cushendall Road as you come into Ballycastle from the east; the name means "foot of the Margy River". It was founded around 1485 by Rory MacQuillan for the Franciscans. You enter through a small two-storey gatehouse with worn steps leading up to the old dormitory, and traces of an altar survive in the church next to it.
The locked vaults hold the remains of the chieftain Sorley Boy MacDonnell and several Earls of Antrim, including Randal MacDonnell, 1st Marquess of Antrim. Legend says the first battle between the MacDonnells and the MacQuillans was fought on the land nearby.